Computer Driver Module for Master Interface to Communication and Control Network

The invention disclosed herein relates to two-way communication and control systems. The following commonly assigned United States patent applications relate to such communication and control systems: Ser. No. 625,747 filed on June 28, 1984 by William R. Verbanets and entitled Multipurpose Digital IC for Communication and Control Network, Ser. No. 625,863 filed on June 28, 1984 by William R. Verbanets and Theodore H. York and entitled Improved Digital ICMicrocomputer Interface Ser. No. 625,862 filed on June 28, 1984 by Leonard C. Vercellotti and William R. Verbanets and entitled Low Error Rate Digital Demodulator now U.S. Pat. No. 4,653,072 Ser. No. 625,864 filed on June 28, 1984 by Leonard C. Vercellotti, William R. Verbanets and Theodore H. York entitled Digital Message Format for Two-Way Communication and Control Network now U.S. Pat. No. 4,644,547; and Ser. No. 769,640 filed on Aug. 26, 1985 by John C. Schlotterer, entitled "Communication And Control Network Master Interface For Personal Computer".

A. Field of the Invention

The present invention relates generally to two-way communication and control systems, and, more particularly, to communication and control systems of the type disclosed in the above identified related applications wherein a communication and control network provides communication between a variety of controlled devices such as circuit breakers, motor starters, protective relays, remote load controllers, lighting systems, and the like, to communicate with and be controlled by a central or master controller over a common network line.

B. Description of the Prior Art

In the communication and control system disclosed in the above identified related applications control and monitoring is carried out over a network consisting of either the existing power lines or dedicated twisted pair wires. The hardware based digital integrated circuit described in detail in the above-identified related applications forms the basic building block for such a communication and control network. This digital IC is a 28 pin semi-custom integrated circuit implemented by complementary metal oxide semiconductor CMOS technique which provides a simple, low cost interface to the communication and control network. This digital IC, which may also be referred to as an industrial communication (INCOM) integrated circuit, or chip, provides the network interface functions of address recognition, detection and storage of an ON-OFF keyed carrier multi-bit message received from the network, carrier generation and transmission of an ON-OFF keyed carrier message to the network in accordance with information stored therein, generation and checking of a five bit BCH error checking code, and framing of the received and transmitted messages.

The digital IC, or INCOM chip, may be configured for one of three operating modes: stand-alone slave, expanded-mode slave, and expanded-mode master. Arbitration of the network is accomplished in a master-slave fashion. The stand-alone slave mode is used by simple devices and provides control of a single output line and the return of two status bits from the slave device. The expanded-mode slave is used to interface microprocessor based equipment to the network and will support far more complex communications between the master and expanded-mode slave. In the expanded-mode master configuration the INCOM device may be used as a direct interface to the master or central computer of the network. However, this master computer must comprise a dedicated computer in order to ensure that messages will not be lost in transmission between an expanded-slave and the master computer. For example, the master computer may send a request to an expanded-mode slave asking for a block of data which will require several 33 bit messages to be sent back to the master. The expanded-mode slave will respond by sending these messages one right after the other. Each 33 bit message will be stored in the shift register of the INCOM chip. However, the entire message must be shifted out of the INCOM shift register during one bit time since otherwise the first bit of the next message may be lost and the next message garbled. Accordingly, when the INCOM chip is used as a direct interface to the network master computer, this computer must necessarily be a dedicated computer in order to guarantee the ability to respond to an interrupt signal from the INCOM chip by shifting out the contents of its shift register within one bit time.

Other bidirectional communication and control systems have also required the use of a dedicated computer as the master computer or controller of the network. For example, in Miller et U.S. Pat. No. 4,367,414 a dedicated computer is interfaced directly to the network by means of a simple interface arrangement which does not involve buffer storage of any kind in the interface.

In Schlotterer application Ser. No. 769,640 filed on Aug. 26, 1985 there is disclosed a hardware interface by means of which a general purpose computer, which may be a personal computer, such as an IBM PC or XT, may be interfaced to such a communication and control network and act as the central or master controller therefore. This hardware interface includes a receive buffer register into which the contents of the INCOM shift register may be rapidly loaded so that the first bit of a succeeding message on the network will not be lost. An interrupt signal is then sent to the processor means of the general purpose computer indicating that a received message has been stored in the interface and can now be read out. The general purpose computer can respond to this interrupt signal and read the message stored in the interface receive buffer at any time during the next 33 bit message while this next message is being stored in the INCOM shift register. After the general purpose computer has read the first message from the interface receive buffer it releases this buffer for storage of the next message from the network by sending a control signal to the hardware interface.

The master hardware interface of the Schlotterer application also includes a transmit buffer register into which the general purpose computer can write a message intended for the network. The interface responds to an initial transmit signal from the general purpose computer by serializing the message written into the transmit buffer register and loading it into the shift register of the INCOM chip when it is available. During this period the hardware-interface produces a status signal which can be read by the general purpose computer so that it will not load a second message into the transmit buffer while the first message is being read out and loaded into the INCOM shift register. Also, as soon as the first message has been loaded into the INCOM chip, the interface supplies an interrupt signal to the general purpose computer so that it can write a second message into the transmit buffer register while the first message is being transmitted over the network by the INCOM device at the relatively low baud rate of the network.

While the hardware interface disclosed and claimed in the above-identified Schlotterer application is suitable for its intended purpose, it is extremely important that the messages sent to this interface from the general purpose computer be accurate and precise. This will be readily apparent when it is realized that the units which are controlled by this general purpose computer acting as a master for the INCOM network may consist of slave devices which simply execute the commands sent to them over the common INCOM network line. Accordingly, if a faulty message is sent out by the master controller, it could cause catastrophic results on the network.

In accordance with the present invention, a driver module is provided in the general purpose computer which cooperates with and drives the hardware interface of the Schlotterer application and also performs a number of error checking functions in connection with each message sent out by the master so that faulty messages are not placed on the INCOM network. Specifically, this driver module, which may be referred to as the INCOM Communication Module (ICM), is arranged to receive command, data or control information in an eight byte string which is passed from the application software via the general purpose computer operating system to the ICM. If all eight bytes are not transmitted to the ICM within a predetermined time interval, it informs the computer of an error and does not transmit the message out to the hardware interface. This prevents a faulty message from being sent out when, for example, only a seven byte string is generated by the application software.

The ICM will buffer up to thirty-two (32) output commands, data or control messages to the INCOM network of eight bytes each and up to thirty-two (32) input or response messages from the network of four bytes each. If an attempt is made to send more than thirty-two output messages, the ICM sends a busy signal to the application software to inform it of the error.

The first byte of the eight byte output message string is a control byte by means of which the application software can designate predetermined succeeding bytes of the string as either a command or data message for the INCOM network or a control message to the hardware interface to change the master address or the baud rate of the INCOM chip associated therewith. The ICM responds to this control byte by reformatting succeeding bytes of the string in the INCOM network format and transmitting the reformatted output message to the hardware interface.

Additional bytes of the eight byte string are employed to establish that one or more responses (up to a maximum of thirty-two) is requested from the addressed slave device on the INCOM network and also establish a timeout interval of variable duration during which a response should be received. The ICM responds to these additional bytes by setting up a timeout interval of the requested duration during which it waits for the response and prevents the transmission of an additional output message even though requested by the application software. If no response is received within the timeout interval, the ICM again tries to establish communication with the slave device by retransmitting the same output message to the hardware interface, if such a retry, or a number of retries, is designated by the application software. If no response is received after one or more retries an error flag is set by the ICM. However, if more than one response is requested by the application software, the ICM forces zero retries even though a retry is requested by the application software. In so doing, the ICM avoids the situation where, for example, three response messages are requested but only one is received during the timeout interval. If the message is retried, duplicate response messages would be stored in the ICM's Rx buffer which could be falsely interpreted by the application software.

When response messages are received from the INCOM network, the ICM adds a fourth status byte to the incoming message to inform the application software of certain conditions. One bit of the status byte is used to inform the application software that the preceding bytes of the received message are not valid. Such a condition can arise when the application software reads from the ICM Rx buffer when no message has been received from the INCOM network but a residue may have been left in this buffer from a previous communication. Another bit of this status byte is used t inform the application software that the requested number of response messages have been received. This bit is set by the ICM when the number of responses requested in the original eight byte string has been received from the expanded mode slave on the INOOM network.

Another bit of this status byte is set by the ICM when more than thirty-two response messages have been received before any message is read out of the ICM Rx buffer which can store only thirty-two such messages. This informs the application software that one or more response messages may have been lost. A further bit of the status byte is set when a timeout error has occurred on a received message to inform the application software that this response message is incomplete. Additional bits of this status byte are used to inform the application software that a message was received with a BCH error and to designate the received message as either data or a command message from the INCOM network.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:

FIG. 1 is an overall block diagram of the hardware interface with which the driver module of the present invention cooperates;

FIGS. 2-6, when placed in the manner shown in FIG. 7 constitute a detailed schematic drawing of the hardware interface of FIG. 1;

FIG. 8 is a series of timing diagrams illustrating the basic timing of the hardware interface of FIG. 1;

FIG. 9 is a series of timing diagrams illustrating the operation of the hardware interface in receiving a message from the communication network;

FIG. 10 is a series of timing diagrams illustrating the operation of the hardware interface during transmission of a message onto the network;

FIG. 11 shows the control message format of the transmit buffer of the hardware interface of FIG. 1;

FIG. 12 shows the network message format for the receive buffer of the hardware interface of FIG. 1;

FIG. 13 shows the control register format of the hardware interface of FIG. 1;

FIG. 14 shows the status register format of the hardware interface of FIG. 1;

FIG. 15 is an overall flow chart illustrating how the driver module of the present invention functions with the operating system of the general purpose computer;

FIG. 16 is a flow chart of the time keeping functions of the driver module of the present invention;

FIG. 17 is a more detailed flow chart of the driver module of the present invention;

FIG. 18 is a detailed flow chart of the operation of the driver module in receiving a message from the hardware interface of FIG. 1;

FIG. 19 is a detailed flow chart of the operation of the driver module in processing an eight byte string developed by the application software of the general purpose computer;

FIG. 20 is a flow chart of the operation of the driver module in taking an output message from the application software and loading it into the TX buffer of the ICM; and

FIG. 21 is a flow chart of the operation of the driver module in supplying a message received from the hardware interface to the application software.

Referring now to the drawings, and more particularly to the block diagram of FIG. 1, the digital IC which is described in detail in the above identified cross referenced applications, is shown in FIG. 1 as the INCOM integrated circuit U3. The INCOM chip U3 is interfaced with the common network line 20 of the communication and control network, through an INCOM coupling circuit 22. The common network line 20 may be power line for the factory, office building or home, or may be a dedicated twisted pair. The coupling circuit 22 is connected to the network line 20 through a connector J2 and provides bidirectional coupling between the INCOM chip U3 and the network line 20 as well as amplifying and limiting a received message placed on the line 20 by another unit of the communication and control network which is also coupled to the line 20. In the alternative, the INCOM chip U3 may be connected to another network medium, such a as fiber optics cable system in which case the fiber optics transmitter/receiver combination may be connected to the connector Jl and an enable signal supplied to this connector is effective to disconnect the INCOM chip U3 from the line 20 and interface it with the fiber optics cable system, as will be described in more detail hereinafter.

As described generally heretofore, the INCOM chip U3 is a 28 pin CMOS semi-custom integrated circuit which provides a simple low cost interface to the communication and control network. The INCOM chip performs the network interface functions of address recognition, detection and storage of an on-off keyed carrier multi-bit message received from the network, carrier generation and transmission of an on-off keyed carrier message to the network in accordance with information stored therein, generation and checking of a cyclic error code, such as a five bit Bose-Chaudhuri-Hocquenguem (BCH) error code, and framing of the received and transmitted messages to the specific format required by the network.

In the hardware interface system disclosed the INCOM chip U3 is operated in the expanded-mode master configuration and is interfaced with a general purpose computer employing the hardware components shown in FIG. 1. Specifically, these hardware components are arranged to interface the INCOM chip U3 to an IBM personal computer (PC or XT) and all of these hardware interface components, including the INCOM chip U3 and the coupling circuit 22 are arranged on a printed circuit board or card, which may be plugged into one of the I/O slots on the IBM processor bus. This printed circuit board or card thus comprises a cocomputer-network interface which will be referred to as a CONI card in the present specification. More particularly, this CONI card is plugged into the IBM processor bus 24 by means of the dual read-out 31/62 pin connector P1 which is the standard connector for the IBM processor bus 24 which includes the address bus 26, the data bus 28 and the control bus 30. The hardware interface CONI card of FIG. 1 is a slave on the computer bus 24 and will only respond to I/O read and write operations. The CONI card is not capable of bus mastership. The size of the I/O address space required for the CONI card of FIG. 1 is 11 bytes, the CONI card responding to I/O addresses in the range 300h-30Ah. The CONI card generates bus interrupt request No. 3 in the IBM nomenclature, this interrupt corresponding to IBM POIS interrupt number "OBh", address "2C-2Fh".

Considering first the electrical interface between the CONI card of FIG. 1, the IBM computer bus 24 and the network line 20, the following definitions will be used:

Considering first the computer bus signal interface (connector P1), these signals are defined by IBM publication 1502234, Chapter 1 and are shown in the following Table 1.

However, because the CONI card is a slave device on the processor bus 24, not all of the bus signals are utilized by the CONI card. A summary of those interface signals which are utilized by the CONI card is as follows:

The INCOM network interface (J2 connector) is a 6 pin modular RJ 126 jack that connects the CONI card to the INCOM network line 20. More particularly, pins 1 and 6 of the J2 connector connect directly to the INCOM network line 20 or through an insolation transformer if this line is a power line. The coupling circuit 22 is a bidirectional transformer coupled circuit which is tuned to the INCOM network carrier frequency of 115.2 kHz. The transformer which isolates the INCOM network from the IBM computer internal circuitry has a high-potential rating of 2500 VAC and a 1 microsecond impulse rating of 6 KV peak. The network wiring 20 is also isolated by series capacitor rated at 0.01 mfd, 2%, 400 V.

In the transmit mode, the open circuit voltage across the INCMM network interface terminals J2-1, J2-6 is less than 30 volts RMS, dropping to approximately 2.5 volts RMS with a 10 ohm resistive load. The short circuit current is approximately 100 milliamps RMS. The transmitter portion of the INCOM chip U3 and coupling circuit 22 can operate continuously without damage with either an opened or shorted load at the network interface terminals. The polarity of the leads connected to the network interface terminals is not important.

In the receive mode the input impedance of the CONI card-network interface as seen by the network looking into the J2 terminals 196 is 10 ohms at the carrier frequency of 115.2 kHz. The receiver sensitivity of the coupling circuit 22 and INCOM chip U3 is 10 millivolts at 115.2 kHz with a band pass response centered at this frequency. The digital carrier detection circuitry within the INCOM chip U3 has a + or -1.5 kHz window.

Considering now the external transceiver connection (J1 connector) to the CONI card of FIG. 1, the J1 connector is a 9 pin female delta subminiature connector that connects the CONI card to an external INCOM network transceiver. This connector is used in applications where higher bit rates are employed or when a non-standard network transceiver is used, as for example a fiber-optic interface. This external interface is active only when a connector present signal is detected on the J1 connector, the pin connections of the J1 connector being shown in Table II below.

J1-1: EXT-RxDATA

J1-2: EXT-TxDATA

J1-3: +5 V

J1-4: +12 V

J1-5: -12 V

J1-6: GND

J1-7: GND

J1-8: GND

J1-9: EXT-ENABLE/

The transmitter output signal on pin J1-1, referred to as EXT-TxDATA, is a standard LS-TTL output that is the high-true transmit data output from the INCOM chip U3 whenever the external transceiver interface is enabled. When this interface is disabled pin J1-2 is low. The receiver input signal J1-1, referred to as EXT-Rx DATA, is a standard LS-TTL input with a 10K ohm pull up to +5 volts. It is used only when the external transceiver is enabled. The external transceiver enable signal on pin J1-9, referred to as EXT-ENABLE/, represents 3 standard LS-TTL input loads with a 10K ohm pull up to 5 volts. When low, the external transceiver is enabled and the internal transceiver circuits in the coupling circuit 22 are disabled.

The operating discipline of the hardware interface CONI card is described by both the electrical and software interfaces of the CONI card. All data and control information from the IBM general purpose computer (PC or XT) is passed through I/O registers located on the CONI card. The CONI card does not respond to processor memory commands. These I/O registers located on the CONI card are located in I/O address space based at 300h. The CONI card will respond to all I/O read and write requests in the range 300h-30Ah.

The I/O registers on the CONI card include a transmit buffer register 40 and a receive buffer register 50. Each of the buffers 40, 50 comprise a dual port register file accessed by both the processor bus 24 and the CONI card hardware. The transmit buffer 40 is written only by the processor interface and is read only by the INCOM network interface. The receive buffer 50 is written only by the INCOM network interface and is read only by the processor interface. More specifically, the transmit buffer 40 consists of 4 byte-wide write only registers 42 which are accessed at I/O addresses 300h through 303h and redundantly at 304h through 307h. The IBM processor writes to these registers by placing data on the data bus 28 which is applied through data bus receivers 44 to an internal data input bus 46 connected to port A of the register file 42. The processor also places a suitable input output address on the address lines 26 and an IOW signal on the control bus 30 which are decoded by the address and command decoder 48. The transmit buffer 40 is read from port B of the register file 42 by means of a multiplexer 52, the register file 42 and multiplexer 52 being controlled during the read out operation by an INCOM read/write state machine 54. The state machine 54 is controlled by a timing generator 56 and provides suitably timed counter pulses CTR[3;0] to the register file 42 and multiplexer 52. The IBM processor should write into the registers 42 only when a message is not in the process of being read out of this register as indicated by the contents of a status register 58. The four register file 42 may be loaded in any order and the contents of the transmit buffer 40 are not altered during the transmit operation. If sections of a message are unchanged from the previous transmission these sections do not have to be reloaded into the transmit buffer 40. A read operation from the I/O locations by the IBM processor will access the corresponding locations in the receive buffer 50 due to the above-described redundant connection.

Messages are written into the transmit buffer 40 in the format of the INCOM communication network, as described in detail in the above identified cross referenced related applications. The format of the transmit buffer 40 is shown in FIG. 11 for a message with the control bit (b2) set. As described in more detail in said related applications, a message with the control bit b2 set ("1") designates a control or command message which the master may send over the common network line 20 to a stand alone slave or an enable-mode slave which includes the address of the slave, an INCOM instruction and other command data. More specifically, referring to FIG. 11, the control bit b2 is written into the most significant bit 7 of the register which is addressed at input output address 300h, the remaining bits of this register being unused. In the next register which is addressed at I/O address 301h, the INCOM instruction bits b3-b5 and the reply request bit b6 are written into the four lower stages of this register. If an expanded mode slave is addressed the four upper stages of this register may contain bits b7-b10 which provide a command to the microprocessor based equipment to which the expanded mode slave is interfaced, as described in detail in said related applications. The next register which is addressed at I/O address 302h contains bits b11-b18 of the control message which are the 8 lower order bits of the address assigned to the slave on the network line 20. In the register addressed at I/O address 303h the four lowest order stages contain bits b19 to b22 of the INCOM message which comprise the 4 highest order bits of the slave address. If an expanded mode slave is addressed, bits b23-b26 of the INCOM message, which is stored in the four upper stages of this register, may contain further commands or data for the microprocessor based equipment to which the expanded mode slave is interfaced.

As described in detail in said related applications, after an interface has been established between an expanded mode slave and the associated microprocessor based equipment, the format of the message transmitted to the slave is changed so as to permit relatively complex communications back and forth between the master and the slaves on the network. Thus, once an interface is established in response to the first command message shown in FIG. 11, subsequent messages may be written into the transmit buffer 40 in which the control bit b2 equals a logic "0". In this data communication message the registers addressed at I/O addresses 301h-303h will each contain data which is supplied from the master IBM processor, through the CONI card, and over the network line 20 to the addressed expanded mode slave.

The message which has been stored in the transmit buffer 40, as shown in FIG. 11, is read from port B of the register file 42 by the multiplexer 52, beginning with the register which is addressed at I/O address 300h. The multiplexer 52 serializes the 8 bits of data available from each register and supplies individual data bits to the bidirectional DATA line which is connected to the internal shift register in the INCOM chip U3. Concurrently, therewith the state machine 54 supplies serial clock pulses over the SCK line to the clock input of the internal shift register in the INCOM chip U3 so that the message shown in FIG. 11 is loaded into this shift register beginning with bit b2 and ending with bit b26, as is described in more detail hereinafter.

Considering now the receive buffer 50, this buffer comprises the register file 60 which consists of 4 byte wide read only registers which are accessed at I/O addresses 304h through 307h and redundantly at 300h through 303h. More particularly, port B of the register file 60 is connected to an internal data out bus 62 DOUT(7:0) to which the output of the status register 58 is also supplied. The IBM processor may read any one of the four registers in the register file 60 by placing the corresponding I/O address on the address bus 26 and an input output write signal IOW on the control bus 30, the address and command decoder 48 decoding these signals and providing a bus gate pulse to the data bus drivers 64 which connect the internal data output bus 62 to the data bus 28 of the IBM processor.

Each message received by the CONI card from the INCOM network is first loaded into the internal shift register of the INCOM chip U3 in the manner described in detail in the above identified related applications. After the network message has been loaded into the INCOM chip U3 it provides an interrupt signal on the INT line to the read write state machine 54 which responds by holding the read write line R/W high and supplying timed serial clock pulses over the SCK line so as to shift the stored message serially onto the bidirectional DATA line and through the four bit shift register 66 to port A of the register file 60. The read/write state machine 54 also controls the loading of data into the register file 60 to enable the use of the four bit shift registers 66, as will be described in more detail hereinafter. As each four bits of the message stored in the INCOM chip U3 are shifted into the register 66 they are supplied over the receive data bus 68 to port A of the register file 60, the read/write machine state machine 54 supplying suitable counter signals to the register file 62 to enable the storage of the received message in the four bit wide registers of the register file 60. Additionally, if the IBM processor attempts to write into the input output locations assigned to the receive buffer 50 this will result in writing into the corresponding locations in the transmit buffer 40 due to the above described redundant input output connections.

The format of the network message which has been loaded into the receive buffer 50 is shown in FIG. 12. Referring to this figure, since the INCOM chip U3 on the CONI card of FIG. 1 is operated in the expanded master mode in which its interface facilities are always enabled, the message shifted out of the internal shift register of the INCOM chip U3 includes 2 additional data bits, the RxTx bit and a BCH error status bit, as described in detail in said related applications. Specifically, the RxTx bit is always set when a message has been received from the network which is to be read out over the enabled interface of the chip U3. Thus, in the register which is read from the I/O address 304h the fifth stage of this register is set to a "1". If the message has been received from the network without an error, as determined by the BCH error checking circuitry in the INCOM chip U3, the BHH error status bit "ber" which is stored in the sixth stage of this register will be a zero. On the other hand, if an error is detected in transmission on the network, the BCH error status bit ber=1. When such a message is read from the receive buffer 50 by the IBM processor the BCH error status bit ber=1 is detected and the received message is not considered valid. The control bit B2 of the receive message is stored in the highest stage of the register addressed at I/O address 304h and the remaining bits of the receive message are stored in the registers addressed at I/O addresses 305h-307h, as shown in FIG. 12.

The hardware interface CONI card of FIG. 1 also includes a control register 70 which is used by the IBM processor to control this hardware interface. More specifically, the control register is connected to the internal data input bus 46 on the CONI card so that data placed on the data bus 28 by the IBM processor may be written into the register 70 through the data bus receivers 44. The control register 70 is assigned I/O address 308h and it may be written to by the IBM processor by placing the desired data on the data bus 28, and I/O address 308h on the address bus 26 and an I/O write signal IOW on the control bus 30. The address and command decoder 48 decodes these address and control signals and provides a gating signal to the control register 70, as will be described in more detail hereinafter.

The format of the control register 70 is shown in FIG. 13. Referring to this figure, bit 0 of the control register is assigned to an initiate transmit signal. After the IBM processor has written a message into the transmit buffer 40 it can produce an initiate transmit signal by writing a "1" in bit zero of the control register 70 (CR:0=1). The CONI card responds to this initiate transmit signal by loading the message stored in the transmit buffer 40 into the internal shift register in the INCOM chip U3 and controlling the INCOM chip U3 over the R/W line to initiate transmission of the message stored in its internal shift register onto the network line 20. During the period when the message stored in the transmit buffer 40 is being transferred to the internal shift register of the INCOM chip U3, bit 1 of the status register 58 is set (SR:1=1) and during this period the CONI card ignores an initiate transmit signal from the IBM processor. Writing a "0" in bit zero of the control register 70 has no effect.

Bit 1 of the control register 70 is an acknowledge receive signal. More particularly, after the IBM processor has read the network message which is stored in the receive buffer 50 the IBM processor can produce an acknowledge receive signal by writing the control register with bit 1 set (CR:1=1). This informs the CONI card that the received message has been read by the IBM processor and that the receive buffer 50 is available for storing the next network message from the INCOM chip U3. Writing a zero to bit 1 of the control register 70 will have no effect.

In order to permit the IBM master to control the baud rate at which messages are transmitted and received by the INCOM chip U3, bits 6 and 7 of the control register 70 re designated as baud rate control bits. A logic 0 in its 6 and 7 will leave the current baud rate unchanged. However, the IBM master can change the baud rate to any one of the three values at which the INCOM chip U3 is designed to operate by writing the appropriate values in bits 6 and 7 of the control register 70. Thus, for CR:7,6=01 the corresponding stages of the control register 70 supply control signals BR0 and BR1 to the INCOM chip U3 which cause it to operate at a baud rate of 38.4 kHz. For a setting of CR:7,6=10 the chip U3 will operate at a baud rate of 1200 Hz and for a setting of CR:7,6=11 the chip U3 will operate at the baud rate of 300 Hz.

It will be noted from the above description of the bits of the control register 70 that these bits are defined so that independent operation of the various functions on the CONI card can share this common control register. This is made possible because zero fields have been defined as having no affect on their associated control function. For example, producing an initiate transmit signal (CR=01h) will not affect operation f the receiver or change the baud rate. This is because writing a zero in the other bits of the control register has no effect.

The status register 50 issued by the CONI card to inform the IBM processor of the state of the CONI card. Status register is read from the same I/O address 308h at which the control register 70 is written to by the IBM processor. The format of the status register 58 is shown in FIG. 14. Referring to this figure, bit 0 of the status register is used as a transmit sequence signal bit which indicates the availability of the transmit buffer 40 to the IBM

In order to permit the IBM master to processor. A logic 1 in bit 0 of the status register (SR:0=1) indicates that the CONI card is transferring the contents of the transmit buffer 40 to the INCOM chip U3 for transmission onto the network 20. During this time the IBM processor should not write to the transmit buffer registers. A logic zero is bit 0 (SR:0=0) indicates that the transmit buffer 40 is available to the IBM processor. After reset, SR:0=0.

Bit 1 of the status register 58 comprises an Rx control bit which indicates the availability of the receive buffer 50 to the IBM processor. A 1 in bit 1 of the status register 58 (SR:1=1) indicates that the CONI card is transferring a message from the INCOM chip U3 to the receive buffer 50. Reading the receive buffer during this time will produce meaningless data. A zero (SR:1=0) indicates that the buffer contains a valid message and the IBM processor may safely read its contents. After reset, SR:1=1 since no message has yet been stored in the receive buffer 50.

Bit 2 of the status register 58 comprises a transmitter interrupt request bit which indicates the completion of the transfer of a message from the transmit buffer 40 to the INCOM chip U3 in response to an INIXMT signal from the IBM processor. This bit will be set (SR2:=1) after the contents of the transmit buffer 40 have been loaded into the INCOM chip U3 and the state machine 54 pulls the R/W line high to initiate transmission by the INCOM chip U3 over the network line 20. At the same time tis bit is set an interrupt request is placed on the IRQ3 line of the control bus 30 (pin B25 of connector P1, table I) as will be described in more detail hereinafter. The transmitter interrupt request bit is cleared (SR:2=0) after the status read operation. It should be noted that the transmission of the message by the INCOM chip U3 over the network will still be in progress at the time the transmitter interrupt request bit is set, the setting of this bit indicating to the IBM processor that the transmit buffer 40 is empty and it may write another message into it although this second message will not be transferred to the INCOM chip U3 until transmission of the first message onto the network is completed and an interrupt is produced on the INT line to the state machine 54.

Bit 3 of the status register 58 is a receiver interrupt request bit which indicates that a message has been received from the INCOM network. This bit will be set (SR:3=1) after the receive buffer 50 has been loaded with message received by the INCOM chip U3. At the same time this bit is set an interrupt request is produced on the IRQ3 line, as will be described in more detail hereinafter. This bit will be cleared (SR:3=0) after the status read operation.

Bits 5, 4 of the status register 58 are baud rate status bits which indicate the current baud rate of the INCOM chip U3. SR:5, 4=01 indicates a baud rate of 38.4 kHz. SR:4, 5=10 indicates a baud rate of 1200 Hz. SR:5, 4=11 indicates a baud rate of 300 Hz. SR:5, 5=00 is illegal.

Bit 7 of the status register 58 is the INCOM busy status bit which indicates the status of the INCOM chip U3. This bit will be set (SR:7=1) whenever the INCOM chip U3 is busy demodulating a network message and storing in its internal shift register or is in the process of transmitting a message which has been stored in this register from the transmit buffer 40 on the INCOM network.

The hardware interface CONI card of FIG. 1 is provided with master address registers 76, 78 into which the IBM processor can write a desired address for the INCOM chip U3. When the ICOM chip U3 is operated in the expanded master mode it should be given an address which is different from that assigned to any of the slaves on the INCOM network. Even though the INCOM chip U3 is able to receive all messages on the network irrespective of their addresses, the address comparison circuit in the INCOM chip U3 is still functioning in the expanded master mode of this chip. Accordingly, the master address setting of the chip U3 should be different from all slaves to avoid a confusing address comparison output signal. The master address may also be changed for other purposes, such as testing, and the like.

The address registers 76, 78 are accessed by the IBM processor through the data bus receivers 44 and the internal data input bus 46. The INCOM address register 76 is a byte wide register to which the IBM processor can write at I/O address 309h. This register contains the 8 lower order bits of the INCOM network address for the CONI card. The INCOM address register 78 is a nibble wide register which contains the high order bits of the INCOM network address for the CONI card, this register also being accessed over the internal data input bus 46. Bits 3 through 0 of this register are bits 11 through 8 respectively of the 12 bit INCOM address of the INCOM chip U3. On reset both of the registers 76 and 78 will be initialized to zero. The IBM processor can write into the INCOM address register 76 by placing the desired byte of data on the data bus 28 and an I/O address of 309h on the address bus 26 together with an IOW signal on the control bus 30. The address and command decoder 48 decodes these address and command signals and supplies a load register signal to the address registers 76. In a similar manner the IBM processor can write into the address register 78 by placing an I/O address of 30Ah on the address bus together with an IOW signal on the control bus 30. The 12 bit output of tee register 76, 78 is supplied to the INCOM chip U3 over the master address bus 80 MADR(11:0) so that the address comparison circuit of the INCOM chip U3 can utilize the INCOM address established by the IBM processor and stored in the register 76 and 78.

The CONI card is initialized by the hardware reset signal "RESET DRV" received from the IBM control -bus 30 (pin B2 of connector P1). However, since the IBM personal computer only provides this reset signal on a power up sequence, the CONI card of FIG. 1 is also arranged to respond to a software reset operation initiated by the IBM processor. More specifically, the address and command decoder 48 is arranged so that a read operation from the I/O address 30Ah by the IBM processor is decoded to initiate a hardware reset of the CONI card. After reset, either by the hardware reset signal from the IBM control bus 30 or a software read operation at I/O address 30Ah, the CONI card will be placed in a state in which the contents of the transmit and receive buffers 40, 50 is indeterminate, the status register 58 contents will be 12h, the baud rate of the INCOM chip U3 will be set at 1200, no message transmission will be in progress, the CONI card will be prepared to receive a message from the INCOM network, and the CONI card address will be set to 00.

Considering now the general operation of the CONI card of FIG. 1 during a transmit operation, whenever a message is to be transmitted the IBM processor checks the status register bit zero (SR:0) to determine if the transmit buffer 40 is available to the IBM processor. A "1" in this bit indicates that the CONI card has not yet completed unloading of previous message from the transmit buffer 40. A zero in SR:0 indicates that the transmit buffer 40 is available and may be filled with a new message. After the transmit buffer 40 has been loaded, the initiate transmit bit in the control register (CR:0) should be set by the IBM processor to request that the message in the transmit buffer be transmitted on the INCOM network. The CONI card will set the transmit sequence bit in the status register (SR:0) in response to the writing of CR:0=1 by the IBM processor. The new transmit message will be loaded in the INCOM chip U3 when it is available. After the message has been loaded into the INCOM chip U3 and transmission to the INCOM network initiated, SR:0 will be reset, an interrupt request is placed on the IRQ3 line of tee control bus 30 and the transmit or interrupt request bit of the status register 58 (SR:2) is set.

The IBM processor can either poll the status register (SR:0) or respond to the interrupt request to determine completion of unloading of the transmit buffer 40 into the INCOM chip U3. Since bit 2 of the status register is reset after the status read operation, the IBM processor must keep track of this completion interrupt. The hardware implementation of this interrupt (SR:2) will only reset the interrupt if it was read as a 1. This prevents clearing the interrupt erroneously if the status read operation and completion of unloading of the transmit buffer 40 occurs simultaneously as is described in detail hereinafter.

The actual message transmission on the INCOM network will continue after the status register update. The INCOM busy signal (SR:7) will remain set until the message has been completely transmitted by the INCOM chip U3. Also, as discussed heretofore, the INCOM busy signal (SR:7) is also asserted by receive operations of the INCOM chip U3.

Considering no the general operation of the CONI card in FIG. 1 during a receive operation, since the INCOM chip U3 is operated in the expanded master mode, the CONI card will receive all messages on the INCOM network except those transmitted by itself. Whenever a message is detected, the INCOM chip U3 will be activated and load the receive message into its internal shift register. If the receive buffer 50 is available at the completion of reception of the message (SR:1=0), the CONI card will transfer the contents of the INCOM shift register to the receive buffer 50, set the receiver interrupt request bit of the status register 58 (SR:3=1), and request an IBM processor interrupt on the IRQ3 line of the control bus 30. If the receive buffer 50 is not available (SR:1=1), the message will remain in the INCOM shift register until the IBM processor has read the message already stored in the receive buffer 50 and then sets the acknowledge receive bit of the control register 70 by writing this control register with bit 1 set (SR:1=1). The CONI card responds to the ACKRCV signal developed by the control register 70 by clearing the status register bit 1 (SR:1).

When the IBM processor responds to the receiver interrupt, or polls the status register (SR:3=1), it may read the message stored in the receive buffer 50 at I/O addresses 304h through 307h. If the IBM processor polls the status register, the SR:3 bit is cleared after reading this register. A status of one (1) in this bit indicates that the CONI card requires service i.e. reading of the message stored in the receive buffer 50. This status must be saved for processing by an appropriate software routine in the IBM processor.

All messages which are read from the receive buffer 50 by the IBM processor will include a BCH error status bit i.e. bit 6 in the register addressed at I/O address 304h (FIG. 12) and the IBM processor should check this BCH status bit and discard the message if this bit is set.

After the message has been read from the CONI card by the IBM processor, the IBM processor must free the receive buffer 50 for additional messages by setting the acknowledge receive bit in the control register (CR:1=1). Failure to release the receive buffer 50 will cause all future network messages to be ignored by the CONI card.

From the above general description of the CONI card of FIG. 1, it will be seen that the processor data bus 28 is received by the data bus receivers 44 and driven by the data bus driver 64. Input data received by the data bus receivers 44 is driven onto the internal input data bus 46. All output data from the CONI card is placed on the internal output data bus 62 (DOUT[7:0]) that is received by the processor data bus drivers 64. These separate unidirectional internal data paths are provided in the CONI card of FIG. 1 to limit loading on the IBM processor data bus 28 and to eliminate bus contention problems which would be created if a bidirectional internal data bus is employed.

In FIGS. 2-6, inclusive, of the drawings a detailed circuit diagram is given of the CONI card which is shown in block diagram form in FIG. 1. The following sections will describe the detailed circuit operation of the CONI card with circuit references to FIGS. 2-6, inclusive. All signal names will be capitalized and terminate with a "/" if the signal is shown in the drawings with an over bar (low-true).

The INCOM coupling circuit on the CONI card is shown in FIG. 2 of the drawings. Referring to this figure, it is first pointed out that a similar coupling circuit is disclosed in Engel et al application Ser. No. 706,079, filed Feb. 27, 1985, assigned to the same assignee as the present invention, and reference may be had to said Engel application for a detailed description thereof. However, for the purposes of the present invention it may be briefly stated that the INCOM coupling circuit 22 includes a coupling transformer 90 having a primary winding 92 which is connected to the common network line through a capacitor 94, the primary winding 92 and capacitor 94 being tuned to the carrier frequency of 115.2 kHz. A secondary winding 96 is also tuned to the carrier frequency by means of the capacitor 98, the winding 96 being connected in series with an FET 100 and a 10 ohm resistor 102 between the +12 volt and -12 volt pins on the processor bus connector P1 of the IBM processor. The INCOM chip U3 (FIG. 3) develops an ON-OFF keyed carrier signal on its TX DATA line which is supplied through a capacitor 103 to the base of a PNP transistor 104 the collector of which is connected through a diode 106 to the gate electrode of the FET 100, as shown, so as to control conduction thereof in accordance with the carrier-on portions of the transmitted message. When the FET 100 is rendered conductive approximately 24 volts is placed across the secondary winding 96 so that a carrier signal is coupled through the transformer 90 and appears on the network line 20 as an ON-OFF keyed carrier signal of approximately 2.5 volts RMS across a 10 ohm load which is sufficient to drive approximately 5,000 stand alone mode or expanded mode slaves connected to the line 20. The diode 106 may be a light emitting type LED and also indicates periods when the INCOM chip U3 is transmitting a message on the network 20. Preferably the LED 106 is mounted on an edge of the CONI card so that it is visible to the user.

The transformer 90 is also provided with a tertiary winding 110 across which a message received from the network 20 is developed and is supplied through a resistor 112 to a comparator 114 which acts as a high gain amplifier for the received signal so that a received ON-OFF keyed carrier signal of approximately 5 volts amplitude is developed in the output of the comparator 114. This amplified and limited received carrier signal is supplied through a tristate output gate 116 to the Rx DATA input line (pin 6) of the INCOM chip U3. In accordance with the present invention, the CONI card is arranged to receive signals from and transmit signals to another communication network medium through the connector J1. This other communication medium, may for example, comprise a fiber optics cable system which includes a fiber optic cable receiver 120 the output of which is connected to pin 1 of the J1 connector, and a fiber optics cable driver 122 whose input is connected to pin 2 of the J1 connector. The units 120, 122 may also receive power and ground signals from the IBM processor bus connector P1 through the connector J1, as indicated in FIG. 2. When an external enable signal is supplied to pin 9 of the J1 connector the tristate output gate 116 is disabled so that signals are no longer received from the network line 20. At the same time a tristate gate 124 is enabled through the inverter 126 so that the message received by the fiber optics cable receiver 120 is supplied through the tristate gate 124 to the Rx DATA input of the INCOM chip U3. During transmission of a message from the INCOM chip U3 the Tx DATA line is supplied to an AND gate 128 the other input of which is supplied from the inverter 126 so that the transmit message generated in the INCOM chip U3 is supplied to the external Tx DATA line (pin 2 of the J1 connector) and to the fiber optic cable driver

The INCOM chip U3 is described in detail in Verbanets application Ser. No. 625,747 filed June 28, 1984 and assigned to the same assignee as the present invention, and reference may be had to this application for a detailed description of the operation thereof. When the INCOM chip U3 is used on the CONI card of the present invention it is operated in the expanded master mode in which pin 27 is grounded and pin 1 is pulled up internally. When operated in this mode, the INCOM chip U3 has its interface lines continuously enabled. These interface lines include an interrupt line (INT) which is an active high output signal which is asserted at the end of a network message reception or at the end of a transmission operation by the INCOM chip U3. The INT line is reset and held low by a logic 1 on the serial clock (SCK) interface line of the INCOM chip U3 (FIG. 1).

The DATA interface line of the INCOM chip U3 is a bidirectional I/O pin whose direction is controlled by the signal on the read-write (R/W) interface line of the chip U3. When the R/W line is a logic high the DATA line is an output. When an interrupt is asserted on the INT line, the DATA pin indicates the cause of the interrupt, the R/W line being held high at this time. A logic high on DATA when the INT is asserted indicates that the interrupt was caused by the receipt of a network message by the INCOM chip U3. A logic 0 on the DATA line indicates the completion of a transmission to the network by the INCOM chip U3. The DATA interface line is also used as a bidirectional data transfer line during a data transfer operation to the receive buffer 50 from the INCOM chip U3 and during a data transfer operation from the transmit buffer 40 to the INCOM chip U3.

The SCK interface line is a serial clock line which is used to clock DATA into or out of the INCOM chip U3 through the DATA line. The quiescent state of the SCK line should be low. The read write (R/W) interface line of the INCOM chip U3 controls the direction of data transfer on the DATA interface line of the chip U3. The R/W line is also used to transfer control of the internal shift register of the INCOM chip U3 from the IBM processor to the INCOM network so that the chip U3 can initiate message transmission on this network. The BUSY/ interface line of the INCOM chip U3 is an active low output that indicates that the INCOM chip U3 is either busy demodulating a 33 bit network received message or is busy transmitting a similar message onto the network. In the CONI card arrangement the BUSY/ line is supplied through the inverters 130 and 132 (FIG. 3) to an LED 134 which is connected in series with the resistor 136 to the +5 volt supply. The LED 134 is preferably edge mounted on the CONI card so as to provide the user with a visible indication of the time periods when the INCOM chip U3 is receiving a message from the INCOM network or transmitting a message onto the network.

All timing and control signals for both transmit and receive operations to the INCOM interface lines are generated by the INCOM read write state machine 54. Furthermore the logic sequences necessary for these transmit and receive operations are generated by a programmable logic array so that the desired sequence of operations is performed by a logic means which is more compact and less expensive than if the same sequence of operations were carried out by discrete logic circuits. More particularly, the INCOM state machine 54 is comprised of a four bit registered PAL sequencer (U8, FIG. 3), a synchronization latch U7, and the four bit counters U4 and U5. Preferably the PAL sequencer U8 is a commercial type PAL 16R4, the synchronization latch U7 is a commercial type 74LS273 high speed 8 bit register, and the counters U4 and U5 are commercial type 74LS163 high speed four bit synchronous counters. The timing generator 56 for the INCOM state machine 54 comprises a four phase Johnson counter timing generator which includes the dual edge triggered flip flop U33 (FIG. 3), preferably commercial type 74LS74 and the NAND gates 140 and 142. The INCOM state machine 54 also receives signals from and transmits signals to the transmitter control and interrupt logic circuits 144, FIG. 6 and the receiver control and interrupt logic circuits 146, as will be described in more detail hereinafter.

The address lines A0-A9 of the IBM processor address bus 26, and those ones of the processor control bus 30 which are used by the CONI card, are buffered in the octal buffers U20 and U23 (FIG. 4) so as to isolate the processor bus lines from internal loading by the CONI card. Preferably, the buffers U20 and U23 are commercial type 74LS244 octal buffers with three state outputs which provide such isolation. Accordingly, the BUS-CLK line of the processor control bus 30 (B20 of P1 connector) is buffered in the unit U23 and is supplied as the CLK line to the timing generator 56 so as to synchronize all of the timing and control signals generated on the CONI card with the IBM processor clock. The input to the timing generator 56 is thus the 210 ns (4.77 MHz) processor clock BUS-CLK. The timing wave forms generated by the timing generator 56 are shown in FIG. 8 wherein the processor clock pulses on the CLK line are shown at FIG. 8(a). The period of the four phase Johnson counter 56 is 840 ns (nanosecnnds) and the output SO (U33-5) of the generator 56 is supplied to the PAL sequencer U8 to advance this sequencer to the next state, these STATE transitions being shown in FIG. 8(d). The SO waveform is shown in FIG. 8(b) which line is also identified as the PALCLK control line. The timing generator 56 also produces the waveform S1 (U33-9) which occurs one bus clock (210 ns) after the rising edge of SO and is used to advance the counters U4 and U5. The S1 waveform is shown in FIG. 8(c) in which it is also identified as the CTRCLK line. The generator 56 also produces the output T2 at the output of the AND gate 140 which is a BUS-CLK period wide pulse (210 ns) which is generated 1 BUS-CLK period after the rising edge S1 waveform. The T2 waveform is shown in FIG. 8(f) wherein it is also referred to as the INCOMCLK line. The T2 waveform is used as a source of serial clock pulses for the SCK line of the INCOM chip U3 during periods when the PAL sequencer U8 develops an enabling waveform. More particularly, the T2 waveform is supplied to the AND gate 148 to which the INCOM clock control waveform (ICC) developed at pin 12 of the PAL sequencer U8 is also supplied. The ICC waveform is developed during periods when a message stored in the internal shift register of the INCOM chip U3 is to be transferred to the receive buffer 50 of the CONI card and also during periods when a transmit message stored in the transmit buffer 40 is to be loaded into the INCOM chip shift register for transmission on the INCOM network, as will be described in more detail hereinafter. The timing generator 65 also develops a T2/ wave form in the output of the NAND gate 142, which is shown in FIG. 8(i) and is employed to control the receive buffer 50 during a write operation from the INCOM chip U3, as will be described in more detail hereinafter.

As described generally heretofore, the sequencer U8 is a programmable array logic (PAL) device which is programmed in accordance with the PALASAM language to implement the necessary logic equations to provide certain states and state transitions necessary to accomplish the loading of DATA into the internal shift register of the INCOM chip U3 and the reading out of data stored in this shift register. The complete PALASAM listing for the sequencer U8 is given APPENDIX A.4. This listing is in accordance with the programmable array logic handbook of Monolithic Memories, 1978, Chapter 4 wherein the procedure used in designing such a PAL is given. The current state of the sequencer U8 is defined by four flip flops contained in this sequencer. These flip flops are labelled A, B, C, and D in the PALASAM listing reproduced in Appendix A.4. The low-true outputs of these four state flip-flops are available on pins 14 through 17 of the sequencer U8. However, only two of these outputs are used externally on the ConI card, i.e. the D flip flop identified as RCV/on pin 17 and the A flip flop identified as PAL14 on pin 14 of the sequencer U8.

There are six valid states defined for the U8 PAL sequencer. The state of the four internal flip flops will be shown as [DCBA] in the following descriptions:

[0000] IDLE--This is the reset state of the state machine 54. This state is used as the "do nothing" wait state.

[1000] R-EC--This is the "receive, enable counter" state. It is used during a receive operation to clock data from the INCOM chip U3 to the receive buffer 50.

[1010] R-C--This is the "receive, clear" state. It is used during a receive operation to generate a signal to the INCOM chip U3 to release its internal shift register so that it can receive another INCOM network message. Specifically, this signal causes the R/W line to the chip U3 to go low and then high.

[0110] X-EC--This is the "transmit, enable counter" state. It is used during a transmit operation to clock data to the INCOM chip U3 from the transmit buffer 40.

[0111] X-W--This is the "transmit, wait" state. It is used during a transmit operation to wait for the INCOM chip U3 to develop an interrupt on its INT line indicating completion of the transmission of a message by the INCOM chip U3 onto the network line 20.

[0101] X-C--This is the "transmit, clear" state. It is used during a transmit operation to supply a single T2 pulse to the SCK input of the INCOM chip U3 to clear the transmit interrupt which the INCOM chip U produces on its INT line after it has completed transmitting a message onto the INCOM network.

The PAL sequencer U8 is programmed to permit the following state transmissions:

The synchronization latch U7 is clocked by the same signal (SO) that is used to advance the sequencer U8. All asynchronous inputs to the state machine 54 are first synchronized by U7 before being presented to the registered PAL sequencer U8. The primary requirement for this synchronization is due to the COUNT/LD combinatorial output (U8-19) from the PAL sequencer U8. This signal must be stable at the leading edge of the S1 signal which clocks the U4, U5 counter in order for this counter to function properly. If the inputs to the PAL sequencer U8 are not stable during the entire sequencer cycle, the counter U4, U5 would be loaded with the incorrect value any time the inputs to the sequencer U8 changed after the leading edge of S1. A secondary requirement for the synchronization latch U7 is to reduce metastability problems caused by set up time violations on the D-input of the internal flip flops in the sequencer U8.

The counter formed by the two four bit counters U4 and U5 is initially loaded with a count value such that this counter will be filled after the required number of bits have been counted. In the case of a receive operation this counter will be loaded with a value to count the 26 bits of the received message as shown in FIG. 12. In this connection it will be noted that the counter starts with the BCH error bit since for a received message the preceding bit is always a "1". In the case of a transmit operation the counter U4, U5 will be loaded with a value such that it will count the 25 bits of a message to be transmitted to the INCOM network before it is filled, as shown in FIG. 11. More particularly, the counter U4, U5 is loaded by the COUNT/LD signal developed by the sequencer U8 in accordance with a count value supplied over the LOAD-VALUE line from the sequencer U8 at the start of a receive or transmit operation. This counter develops the timing signals CTR0, CTR1, CTR2, CTR3, and CTR4 on the first five outputs thereof. The CTR3 and CTR4 timing signals are supplied to the transmit buffer 40 to control the write operation therefrom and to the receive buffer 50 to control the read operation into this buffer, as will be described in more detail hereinafter. The CTR0, CTR1, and CTR2 signals are employed to time the operation of the multiplexer 52, as will be described in more detail hereinafter. When the counter U4, U5 is filled it supplies a signal over the CTR FF line to the sequencer U8.

Considering now the operation of the INCOM read write state machine 54 during a receive operation from the INCOM network, this operation begins with the presence of a message on the INCOM network line 20. When the INCOM chip U3 detects a carrier on its Rx DATA line it pulls its BUSY/ line low and begins decoding the incoming bit stream and stores the message in its internal shift register. After the final bit of the message has been decoded, the INCOM chip U3 will pull the BUSY/ line high and produce an interrupt signal (high) on the INT line.

The states and state transitions of the INCOM read write state machine 54 during the receive operation are shown in the timing diagram in FIG. 9(b). As shown by this timing diagram, the sequencer U8 idles in a [0000] [0000] state loop. When (1) the INT line is pulled high by the INCOM chip U3, as shown in the timing diagram FIG. 9(d), (2) the DATA line of the INCOM chip U3 is a logic 1 indicating that the interrupt on the INT line is a receive interrupt, and (3) the RxCTL line to pin 6 of the sequencer U8, which is developed in the receiver control and interrupt logic 146 as will be described in more detail hereinafter, indicates that the receive buffer 50 is available; the state machine 54 will initiate a receive operation. The receive operation begins in state [0000] with LOAD-VALUE (U8-13) low (FIG. 9(n)). This will load the U4, U5 counter with 11100100b, as shown in the timing diagram in FIG. 9(p). The next state of the U8 sequencer will be [1000], as shown in FIG. 9(b). In this state the ICC output from the sequencer U8 is high so that the AND gate 148 supplies T2 pulses to the serial clock line SCK of the INCOM chip U3, as shown in the timing diagram of FIG. 9 (m). Also, when the sequencer U8 is in the [1000] state the U4, U5 counter is enabled for counting by the signal on the COUNT/LD output line of the sequencer U8, as shown in FIG. 9(o). Accordingly, the INCOMCLK pulses shown in FIG. 9(m) begin shifting the received message out of the internal shift register of the INCOM chip U3 and onto its DATA line starting with the BCH bit, as shown in FIG. 9(f). The message shifted onto the DATA line is supplied to the shift register 66 and written into the receive buffer 50 in the manner described in detail hereinafter.

The sequencer U8 will remain in the [1000] state until the entire message has been shifted out of the INCOM chip U3 as determined by the setting of the U4, U5 counter. When message bit 26 has been read from the INCOM chip U3, CTR=FF will be asserted by the counter line U5-15 and the sequencer U8 responds thereto by advancing to the state [1010], as shown in the timing diagrams in FIGS. 9(b),(e) and (p). In the [1010] state the sequencer U8 produces a R/W signal on its pin 18 which pulls the R/W pin 25 of the INCOM chip U3 low and then high, as shown by the timing diagram in FIG. 9(l). This signal causes the INCOM chip to condition its internal shift register to receive additional messages from the INCOM network. After state [1010], the U8 sequencer will return to the IDLE state [0000], as shown in FIG. 9(b).

Considering now the operation of the INCOM read write state machine 54 during a transmit operation from the transmit buffer 40 to the INCOM network, prior to initiating such a transmit operation the IBM processor will have loaded a message into the transmit buffer 40, as described generally heretofore. Transmission is initiated by the IBM processor by writing bit 0 of the control register 70 (CR:0=1) and then transmitter control and interrupt logic 144 responds to this write operation by generating an XMTREQ signal, as will be described in more detail hereinafter. The XMTREQ signal is synchronized in the latch U7 and is supplied to pin 7 of the sequencer U8 to cause this sequencer to leave its idle loop [0000] [0000] and begin the transmit sequence if a receive operation is not in progress. The waveforms developed during a transmit operation are shown in FIG. 10 and the state and state transitions of the sequencer U8 during a transmit operation are shown in FIG. 10(b). As shown in this timing waveform, the first transmit state after IDLE [0000] is [0110]. The U4, U5 counter is loaded with 11100110b during the last [0000] state prior to [0110], as shown in FIGS. 10(n) and 10(p). This counter is enabled to count by the signal on the COUNT/LD line at the beginning of the first [0110] state, as shown in FIG. 10(o). During the [0110] state the sequencer U8 pulls its R/W output line low (FIG. 10(l)) and the INCOM chip U3 responds thereto by connecting the bidirectional DATA line to the input of its internal shift register and connecting the SCK line to the clock input of this shift register, as described in detail in said copending Verbanets application Ser. No. 625,747. At the same time the sequencer U8 provides an enabling signal on its ICC line so that the T2 pulses from the timing generator 56 are supplied as serial clock pulses to the SCK input of the INCOM chip U3 as shown in FIG. 10(m). Accordingly, data which is stored in the transmit buffer 40 is serialized in the multiplexer 52 and is loaded into the INCOM chip U3 through the bidirectional DATA line in a manner to be described in more detail hereinafter.

The sequencer U8 will remain in the [0110] state until the U4, U5 counter reaches FFh (CTR=FF) at which time the last bit of the transmit message has been loaded into the INCOM chip U3 as shown by the timing waveforms FIG. 10(f), (g) and (p). The U8 sequencer will then advance to state [0111]. When the U8 sequencer advances to state [0111] the R/W line is pulled high and the INCOM chip U3 responds thereto by initiating transmission of the message stored in its iinternal shift register onto the network line 20 in the manner described in detail in said copending Verbanets application Ser. No. 625,747. This transition of the R/W line is shown in FIG. 10(l). During such transmission the BUSY/ line of the INCOM chip U3 is pulled low, as shown by the timing waveform in FIG. 10(c). During the transition from state [0110] to [0111] the sequencer U8 provides a signal on its PAL14 output line which is employed by the transmitter control and interrupt logic 144 to generate a transmit interrupt on the IRQ3 line of the IBM processor bus to indicate that the message has been loaded from the transmit buffer 40 to the INCOM chip U3, as will be described in more detail hereinafter.

After the INCOM chip U3 has completed transmitting the message stored in its internal shift register onto the INCOM network it produces a transmit interrupt on its INT line, as shown in FIG. 10(d) which causes the U8 sequencer to advance from the [0111] state to the [0101] state, as shown in FIG. 10(b). In the [0101] state the sequencer U8 controls the ICC line so that a single clock pulse is supplied to the SCK input of the INCOM chip U3, as shown in FIG. 10(m), and the INCOM chip U3 responds thereto by removing the transmit interrupt from its INT line and conditioning its internal shift register to receive a message from the INCOM network. From the [0101] state the sequencer U8 will return to the IDLE state [0000], as shown in FIG. 10(b).

The address and command decoder 48 comprises the programmable logic arrays U19 and U21. Preferably the array U19 is a type PAL16L8A and the array U21 is a commercial type PAL 16H8A. A detailed PALASAM listing of the PAL U21 is given in Appendix A.3 together with the function table which is used by the PALASAM language to simulate the logic and to check it, as well as the simulated function table which is used in creating the PAL U21 and testing it. The decoder U21 receives the buffered addresses PA0-PA9 from the buffer U20 corresponding to the conductors A0-A9 of the IBM processor address bus 26, an IRD/ signal which is the buffered input output read signal IOR/ from the buffer 23, an IWT/ signal which corresponds to the input output write (IOW/) signal from the buffer U23 and the DAEN signal which corresponds to the address enable (AEN) signal from the buffer U23. A SELECT signal (U21-19) is decoded from BA5-BA9 and BAEN to define the base I/O address for the CONI card. The SELECT signal is supplied to the PAL U19 for additional registered decoding. The PAL U21 also provides a decoded reset command signal R-CMND in response to the IBM processor performing a read operation at the I/O address 30Ah. The R-CMND signal is OR'd with the buffered RESET-DRV signal from the buffer U23 in the OR gate 150, this signal being further buffered in the buffer U23 and provided as the RESET/ signal to the indicated portions of the CONI card. Accordingly, the CONI card can be reset by the IBM processor when it produces a RESET-DRV signal on the pin B2 of the P1 connector on power up, or, in the alternative, the IBM processor can perform a read operation at I/O address 30Ah to which the PAL U21 will respond by providing a hardware reset signal on the RESET/ line.

The PALASAM listing for the PAL U19 is given in Appendix A.2 and includes the function table used by the PALASAM language to simulate the desired logic and check it, as well as the simulated function table which is used in making and testing the PAL U19. The PAL U19 generates low-true decodes from the buffered addresses BA0-BA3, the SELECT line from the PAL U21 and the IRD/ and IWT/ lines from the buffer U23. In response to these input signals the PAL U19 generates a load memory signal LDMEM/ which is supplied to the transmit buffer 40 to enable the IBM processor to write to this buffer. The PAL U19 also develops a memory read signal MEM-READ which is supplied to the receive buffer 50 to enable the IBM processor to read this buffer. The PAL U19 also generates upper and lower master address load signals LDMAU/ and LDMAL/ which are supplied to the master address registers 78 and 76, respectively to enable the IBM processor to write into these registers. The PAL U19 also generates enabling gate signals for the status register 58, the control register and decoder 70 and the data bus driver 64 on the SRGATE/ line, the CR-GATE/ line and the BUS-GATE/ line, respectively.

The control register and decoder 70 comprises a four bit registered PAL U14, preferably of the commercial type PAL16R4 the PALASAM listing for the logic contained in U14 is given in Appendix A.1 together with the state flip-flop input equations, the function table used by the PALASAM language to simulate the desired logic and check it, and the simulated function table which is employed to manufacture and test the unit. The PAL U14 receives the buffered data input lines DIN [7, 6, 1, 0] on the internal unidirectional data input bus 46 and it decode the IBM processor commands for initiating transmission (INIXMT/) and acknowledging message reception (ACKRCV/). The control register and decoder 70 also contains the baud rate register and associated logic for providing the BR0 and BR1 output signals to control the baud rate at which the INCOM chip U3 operates.

The internal 4 state flip-flops of the PAL U14 are available externally in low-true (complemented) form on pins 14 to 17 of U14. Two of these outputs (BR0 and BR1) are used externally as the baud rate register. The other two (A and B) are only used internally to generate a CR-GATE/ delayed by 2 CLK cycles. It is necessary to generate a leading edge delay on the gating signal CR-GATE/which is developed by the PAL U19 so that processor data (DIN[7:0]) will be stable on the leading edge of the enable that generates INXXMT/ and ACKRCV/ from the decode of the processor address and data. The CR-GATE/ signal is generated in the PAL U21 in response to processor bus signal IOW/. However, the IOW/signal is generated from the "early write" decode in the IBM processor and the data bus (DO-D7) is not stable at the leading edge of IOW/ and consequently is not stable at the leading edge of the CRGATE/signal.

The state flip-flops A and B of the PAL U14 are used to delay the SR-GATE/ signal by two cycles of the processor BUS-CLK. These two flip-flops are connected to form a shift register with the internally generated signal CR-GATE as the serial input. The reset term on both flip-flops is either the reset input pulse on the RESET/ line or the input signal CR-GATE/ from the PAL U19. Accordingly, a delay of only the leading edge of the CR-GATE/ signal is produced in the PAL U14.

The INIXMT/ output from the PAL U14 is a combinatorial decode of the processor data bus, CRGATE/ and CR-GATE/ delayed. The ACKRCV/ output from the PAL U14 is a combinatorial decode of the processor data bus, CR-GATE/ and CR-GATE/ delayed.

The two state flip-flops BR0 and BR1 in the PAL U14 are used as the baud rate register. The input coding of the PAL U14 is arranged to provide the following logical functions:

1. Reset the baud rate register (C & D state flip flops) to 10b. (Baud rate of 1200)

2. Maintain the current state of the register in the absence of a CR-ATE strobe command.

3. Load the register with the appropriate value when CR-GATE is asserted, and either D0 or D1 are non-zero. (shouldn't this be D6 and D7?)

It should be pointed out that the INIXMT and ACKRCV which are in the control register and decoder 70 are not stored in this register but instead are stored separately in the transmit control and interrupt logic 144 and receiver control interrupt logic 146. Such an arrangement permits the control register to be used for the different independent functions described heretofore in which zero fields have been defined as having no affect on their associated control function.

As discussed generally heretofore the interface between the CONI card and the IBM processor is based on two control signals or flags which are generated by the CONI card and supplied to the status register 58 so that the IBM processor can read these control signals. The interface also includes two interrupt sources on the CONI card which are supplied to the processor bus interrupt request line IRQ3. The receiver control and interrupt logic 146 generates one of these controls and is the source of one of these interrupts. Specifically, the logic circuits 146 include a flip-flop U36-5 which is employed to develop the control signal labeled RxCTL which is supplied to the status register as bit 1 wherein it is identified as the Rx control bit in FIG. 14. The flip flop U36-5 is set by the rising (trailing edge) of the RCV/ waveform (FIG. 9h) which is developed by the U8 sequencer at the end of a receive operation in which the message received by the INCOM chip U3 is stored in the receive buffer 50. The RxCTL signal thus indicates to the IBM processor that the receive buffer 50 contains a receive message that is awaiting processing by the IBM processor. It will be noted that the low-true output of the flip flop U36 is used as the RxCTL control signal or flag. Accordingly, this control signal is clear (U36-5 set) when the receive buffer contains a receive message that is awaiting processing. The RxCTL signal is set (U36-5 cleared) by either the reset signal on the RESET/ line or by the ACKRCV signal which is generated by the PAL U14 in the control register and decoder 70 in response to the writing of an acknowledge receive signal into bit 1 of this control register by the IBM processor. Specifically, the flip flop U36-5 is cleared by either the RESET/signal or the ACKRCV/ signal through the OR gate U30-3.

Concurrently with the development of the RxCTL/ signal by the flip flop U36-5, the interrupt logic 146 also develops a receive message request on the IRQ3 processor bus. More particularly, the rising (trailing) edge of the RCV/ signal developed by the sequencer U8 at the completion of a receive operation also sets flip flop U36-9 the Q/ output of which is supplied through the NAND gates 160 and 156 and the tristate driver 158 to the IRQ3 interrupt line of the processor control bus 30.

The receive message interrupt is removed from the IRQ3 line during a status read operation of the status register 58 by the IBM processor. More particularly, the flip flop U35-9 is used to clear the interrupt flip flop U36-9 during a status read operation. The flip flop U35-9 is clocked by the leading edge of the status read gate signal SR GATE/which is developed by the PAL U19 in response to an IOR/ read by the IBM processor at I/O address 308h assigned to the status register 58. This SR GATE/signal is inverted in the inverter 160 and is applied to the clock input of the flip flop U35-9 so as to load this flip flop with the state of the interrupt flip flop U36-9. NAND gate U26-6 is used to clear the interrupt flip flop U36-9 during a status read if U36-9 was set prior to the read operation. More particularly, the SR GATE signal is applied to one input of the NAND gate U26-6 and the Q output of U35-9 is applied to the other input of this NAND gate. The output of the NAND gate U26-6 is supplied through the OR gate U30-8 to clear the interrupt flip flop U36-9. This circuitry permits the receive interrupt flag to the read as a "1" only once, and then automatically clears this interrupt request.

The circuitry 146 resolves the problem of the status read operation and the interrupt set condition occurring simultaneously. The receive interrupt flag is read and cleared only if it was asserted prior to the status read operation. If the interrupt request flip flop U36-9 is set during the status read operation, the interrupt will be read as a zero and the receive request will not be cleared. This can readily be seen by assuming first that when the status read operation occurs a receive interrupt has not occurred. Under these conditions, the flip flop U36-9 will be reset and pin 9 of U36-9 will be low which means that the flip flop U35-9 will also be reset, so that one input of the NAND gate U26-6 will also be low. Next, if it is assumed that an interrupt has occurred and then the status read operation occurs, when the interrupt occurs U36-9 is clocked true by the RCV/signal developed by the sequencer U8 at the end of the receive operation. However, the SELECT line from the PAL U21, which is applied to the pin 13 of the flip flop U35-9, is normally low until the status read operation is initiated by the IBM processor and the right I/O address applied to the address lines A0-89. Accordingly, the flip flop U35-9 is held low and cannot respond to the setting of the flip flop U36-9 on a receive interrupt. When a status read operation occurs the SR-GATE/ signal, which is developed by the PAL U19 starts with the SELECT line high since the SELECT signal is developed first by the PAL U21 in response to the base I/O address of the CONI card. Accordingly, the leading edge of the SR-GATE/ signal occurs while the SELECT line is high and hence the SR-GATE/ signal clocks the flip flop U35-9 and loads it with the state of the interrupt flip flop U36-9. Thus, if the flip flop U36-9 is set, the flip flop U35-9 will be set. When the flip flop U35-9 is set both inputs to the NAND gate U26-6 are high and its output clears the flip flop U36-9 and clears the receive interrupt. Accordingly, if the interrupt signal is read as a "1" it is cleared. At the end of the status read cycle the SELECT line goes low and clears the flip flop U35-9.

The above assumed conditions are the only ones that can occur. If it is assumed that the SRGATE/ and the CRV/ signals occur at the same time U35-9 is either clocked true or it is not clocked true depending upon the state of U36-9. If the RCV/signal is earlier than the SR-GATE/ signal then U36-9 is set. However, if the RCV/signal is later than the SR-GATE/, U35-9 is not clocked true and so will not clear U36-9 with the result that the interrupt is read as a zero and the interrupt request will not be cleared.

The flip flop U35-9 also develops the RxINT signal which is supplied t the status register 58 as bit 3, this bit being identified as the "receiver interrupt request" in FIG. 14, as described previously in connection with this figure.

The transmitter control and interrupt logic 144 is shown in FIG. 6 and operates quite similarly to the logic 146 described in detail heretofore. This logic includes the flip flop U34-5 which is set in response to the transmit initiate signal INIXMT/which is developed by the PAL U14 when the IBM processor requests initiation of a transmit operation from the transmit buffer 40 to the INCOM chip U3. Setting of the flip flop U34-5 generates the XMTREQ signal which is supplied to the U8 sequencer in the state machine 54 and indicates that a transmission operation should be initiated by the sequencer U8. The flip flop U34-5 is cleared by either the reset signal on the RESET/ line or the falling edge of the PAL14/ signal (FIG. 10(k)) which is developed by the sequencer U8 at the end of the transmit operation, this signal being inverted in the inverter 162 and applied to the clock input of the flip flop U34-5. The XMTREQ/ control signal or flag is thus set by the IBM processor writing a transmit initiate signal into the control register 70 and is cleared by the U8 sequencer after the message has been loaded into the INCOM chip U3 for transmission onto the INCOM network.

At the time that the flip flop U34-5 is reset, the transmit interrupt flip flop U34-9 will be set by the rising (leading) edge of PAL 14. The Q/output of U34-9 is supplied through the NAND gate 156 to the IRQ3 line on the IBM processor bus thus indicating to the IBM processor that the message has been loaded from the transmit buffer 40 into the INCOM chip and that another message may be loaded into the transmit buffer 40. The transmit interrupt flip flop U34-9 is cleared by either the RESET/signal or a status read operation, the flip flop U35-5 being employed in a manner identical to that described in detail heretofore in connection with the flip flop U35-9 to clear the flip flop U34-9 after a status read operation. The flip flop U35-5 also develops the TxINT which is supplied to the status register 58 as bit 2 thereof, this bit being identified as the "transmitter interrupt request" in FIG. 14.

The status register 58 comprises a tristate bus driver U16 (FIG. 4) which is preferably of the commercial type 74LS244. This driver is enabled by the SR-GATE/ signal developed by the PAL U19 during a status read operation and gates internal status signals f the CONI card onto the unidirectional internal data out bus DOUT[7:0] 62. The specific status signals which can be read by the IBM processor are the XMTREQ and TxINT signals developed by the transmitter control and interrupt logic 144, the RxCTL and RxINT signals developed by the receiver control and interrupt logic 146 and the baud rate signals BR0 and BR1 stored in the state flip flops of the PAL U14.

The master address register 76, 78 comprise the latches U12 and U13, respectively which are preferably of the commercial type 74LS273 high speed eight bit registers with clear. The 12 bit address of the INCOM chip U3 is contained in the byte wide register U12 and the nibble wide register U13 which are loaded from the internal data input bus DIN[7:0] 46 by the clock signals LDMAL/ and LDMAU/ generated by the PAL U19. The 12 bit output of the registers U12 and U13 is supplied over the master address bus MADR[11:0] 170 (FIG. 5) to the address inputs A0-A11 of the INCO chip U3. The registers U12 and U13 are reset by the RESET/ signal which is developed as described in detail heretofore.

The transmit buffer 40 consists of two dual-port 4.times.4 register file integrated circuits U24 and U25. Preferably these circuits are of the commercial type 74LS670 the register files U24 and U25 are organized as a four word by eight bit dull-port random access memory. The write port of the registers U24, U25 is connected to the internal data input bus 46. Addresses BA0 and BA1 for the write port are supplied by the buffered processor address bits A0 and A1. Write enable is generated by the LDMEM/ signal developed by the PAL U19.

The read port of the registers U24 and U25 is the source of the Tx-DATA[7:0] bus (FIG. 5) which is supplied to the multiplexer 52. The address bits for the read operation from the transmit buffer 40 are supplied by the counter signals CTR3 and CTR4 developed by the counters U4 and U5.

The multiplexer 52 comprises the integrated circuit U2 which is preferably a commercial type 74LS253 dual four-input multiplexer with three state outputs. The multiplexer U2 is employed to serialize the data read from the transmit buffer 40, the output of this multiplexer being supplied to the bidirectional serial DATA input of the INCOM chip U3. The SELECT lines S0 and S1 of the multiplexer U2 are controlled by the timing signals CTR0 and CTR1 which are developed by the interface sequencer counter U4. However, the output enable lines OEA/ and OEB/ of the multiplexer U2, which are controlled by the timing signal CTR2 and CTR2/ from the counter U4, are delayed by the flip flop U38-5 to avoid conflicts with the INCOM chip U3 on the DATA line.

The receive buffer 50 consists of two dual port 4.times.4 register file integrated circuits U17 and U18 which are preferably of the commercial type 74LS670. The register files U17 and U18 are organized as a four word by eight bit memory for read operations by the IBM processor and as an eight word by four bit memory for write operations from the INCOM chip U3. The read port of the registers U17 and U18 is connected to the unidirectional data out bus 62 and is enabled onto the bus by the MEM-READ/signal which is generated by the PAL U19. Addresses for the read port (BA0 and BA1) are supplied by the buffer processor address bits A0 and A1. Write port addresses are provided by the timing signals CTR3 and CTR4 which are generated by the sequencer counter U4.

The write ports of the registers U17 and U18 are driven by the shift register 66 which comprises the integrated circuit U1 preferably of the commercial type 74LS395, the four bit output of the shift register 66 forming the RCV-DATA bus 68 which is supplied to the registers U17 and U18. The shift register 66 is continuously clocked by the timing signal S1 generated by the timing generator 56 and shown in FIG. 8(c). Accordingly, the data on the bidirectional DATA line of the INCOM chip U3, which is applied to the serial input S1 of the shift register 66, is continuously shifted through the register 66. However, this data is not written into the receive buffer 50 from the RCV-DATA bus 172 until a receive operation is initiated by the PAL sequencer U8. More particularly, the timing signals CTR0, CTR1 and CTR2 are applied to a four input NAND gate 174 the other input of which is the RCV/ signal developed by the sequencer U8 which is inverted in the inverter 176. Accordingly, the qualifying signal WEHI/ is developed in the output of the NAND gate 174 only during the period when the sequencer U8 develops the RCV/ signal during a receive operation, as shown in FIG. 9(h). In a similar manner the counter signals CTR0, CTR1, and the counter signal CTR2 which is inverted in the inverter 178, are applied to three inputs of the four input NAND gate 180 to the other input of which the RCV signal is supplied so that the qualifying signal WELO/ is developed in the output of the NAND gate 180. The WEHI/ and the WELO/ signals are applied respectively to the AND gates 182 and 184 to the other input of which the T2/ signal (FIG. 8(i)) developed by the timing generator 56 is supplied. The outputs of the AND gates 182 and 184 alternately write the four bit output of the shift register 66 on the receive data RCV-DATA bus 68 into the registers U17 and U18. This operation is shown in the timing diagrams of FIGS. 9(q) and 9(r). More particularly, as shown in FIG. 9(f) the DATA line is a "1" when a message has been received by the INCOM chip U3, as shown in FIG. 9(f). If no receive operation is initiated by the sequencer U8, a series of ones would continue to be shifted through the shift register 66. However, after the message has been received the INCOM chip U3 produces an interrupt signal on the INT line and the sequencer U8 responds thereto by initiating a receive operation in which clock pulses are supplied to the serial clock line SCK of the INCOM chip U3 as shown in FIG. 9(m). These clock pulses shift the bits stored in the INCOM shift register onto the data line beginning with the BCH bit, as shown in FIG. 9(f). Since only the first three bits of the received message are to be stored in the first byte of the receive buffer 50 which is addressed at I/O address 304h, as shown in FIG. 12, the AND gate 182 produces a write pulse 190 (FIG. 9(r)) as soon as the first three bits have been shifted into the shift register 66 from the DATA serial input line. After the next 4 bits of the received message have been shifted into the register 66, i.e. bits b3, b4, b5 and b6 (FIG. 12) the AND gate 184 produces a write pulse 192 (FIG. 9(r)) so that these bits are written into the register U17. In a similar manner successive groups of four bits of the received message are stored in the registers U17 and U18, the final four bits, b23, b24, b25 and b26, being written into the register U18 by the write pulse 194, as shown in FIG. 9(q) and FIG. 9(r). In this connection it will be noted that FIG. 9(b) shows the change in setting of the counter U4, U5 as the received message is shifted ut of the shift register of the INCOM chip U3.

The IBM processor read and write operations utilize the internal data paths DIN[7:0] an DOUT[7:0] for data transfer. Address and command decode is provided by the PALs U19 and U21 as described in detail heretofore.

A processor read operation is initiated by placing the proper address on the address bus A9-A0. The bus control line IOR/ is asserted, requesting the data from the CONI card. PAL U21 decodes the higher order (A9-A5) addresses and asserts SELECT to the PAL U19. PAL U19 uses SELECT and the lower order (A4-A0) addresses in addition to the buffered IOR/ signal (IRD/) to generate the appropriate enable signal to gate the requested data onto the internal DOUT[7:0] bus. PAL U19 also enables the data bus driver 64 over the BUS-GAEE/ line. The data bus driver 64 comprises the buffer U15 (FIG. 4) which is preferably the commercial type 74LS244. The read operation does not require processor wait states.

A processor write operation is initiated by placing the proper address on the address bus A9-A0. The bus control line IOW/ is asserted, indicating that the write address is stable. Because the IBM processor uses the "early write" signal to generate the bus signal IOW/, data will not be stable prior to the leading edge of IOW/. PAL U21 decodes the higher order addresses and asserts SELECT to PAL U19. PAL U19 uses SELECT and the lower order addresses in addition to the buffered IOW/ signal (IWT/) to generate the appropriate write enable signal to write data from the internal DIN[7:0] bus. Write data is stable at the trailing edge of IOW/ and will be latched at that time in the appropriate memory or register.

In accordance with the present invention, a driver module is provided in the IBM PC which cooperates with and drives the CONI card and also performs a number of error checking functions in connection with each message sent out by the master so that faulty messages are not placed on the INCOM network. This software driver module is referred to as the INCOM Communication Module (ICM). The listing of the ICM is given in the attached Appendix B and flow charts showing the operation of this driver module are given in FIGS. 15 to 21, inclusive.

The ICM is arranged to receive command, data or control information in an eight byte string which is passed from the application software via the general purpose computer operating system to the ICM. If all eight bytes are not transmitted to the ICM within a predetermined time interval, it informs the computer of an error and does not transmit the message out to the CONI card. This prevents a faulty message from being sent out when, for example, only a seven byte string is generated by the application software.

The ICM will buffer up to thirty-two (32) output commands, data or control messages to the INCOM network of eight bytes each and up to thirty-two (32) input or response messages from the network of four bytes each. If an attempt is made to send more than thirty-two output messages, the ICM sends a busy signal to the application software to inform it of the error.

The first byte of the eight byte output message string is a control byte by means of which the application software can designate predetermined succeeding bytes of the string as either a command or data message for the INCOM network or a control message to the CONI card to change the master address or the baud rate of the INCOM chip associated therewith. The ICM responds to this control byte by reformatting succeeding bytes of the string in the INCOM network format and transmitting the reformatted output message to the CONI card.

Additional bytes of the eight byte string are employed to establish that one or more responses (up to a maximum of thirty-two) is requested from the addressed slave device on the INCOM network and also establish a timeout interval of variable duration during which a response should be received. The ICM responds to these additional bytes by setting up a timeout interval of the requested duration during which it waits for the response and prevents the transmission of an additional output message even though requested by the application software If no response is received within the timeout interval, the ICM again tries to establish communication with the slave device by retransmitting the same output message to the CONI card, if such a retry, or a number of retries is designated by the application software. If no response is received after one or more retries an error flag is set by the ICM. However, if more than one response is requested by the application software, the ICM forces zero retries even though a retry is requested by the application software. In so doing, the ICM avoids the situation where, for example, three response messages are requested but only one is received during the timeout interval. If the message is retried, duplicate response messages would be stored in the ICM's Rx buffer which could be falsely interpreted by the application software.

When response messages are received from the INCOM network, the ICM adds a fourth status byte to the incoming message to inform the application software of certain conditions. One bit of the status byte is used to inform the application software that the preceding bytes of the received message are not valid. Such a condition can arise when the application software reads from the ICM Rx buffer when no message has been received from the INCOM network but a residue may have been left in this buffer from a previous communication. Another bit of this status byte is used to inform the application software that the requested number of response messages have been received This bit is set by the ICM when the number of responses requested in the original eight byte string has been received from the stand-alone or expanded work slave on the INCOM network.

Another bit of this status byte is set by the ICM when more than thirty-two response messages have been received before any message is read out of the ICM Rx buffer which can store only thirty-two such messages. This informs the application software that one or more response messages may have been lost. A further bit of the status byte is set when a timeout error has occurred on a received message to inform the application software that this response message is incomplete. Additional bits of this status byte are used to inform the application software that a message was received with a BCH error and to designate the received message as either data or a command message from the INCOM network.

The ICM is written for use on the IBM PC or XT Computer with IBM PC DOS Ver. 2.10 operating system and with the CONI card in one of the spare card slots in the IBM PC. The ICM complies with the standards given in IBM 1502234, Technical Reference Manual, IBM 6024120 DOS Vrr. 2.10 Operating Manual, and IBM 6024125 DOS Ver. 2.10 Technical Reference Manual. The following definitions and abbreviations are used in the ICM specification described hereinafter:

binary numbers:

(base 2) are written with "b" following the number: 0111b=7.

bit numbering:

bits will be specified with the least significant bit designated as 0.

byte:

an eight bit word.

DOS:

Disk Operating System. In this specification, refers to the IBM PC personal computer operating system. disk:

Either a floppy diskette or hard disk in the IBM computer The mass storage of data and or programs.

File:

A group of related data treated as a unit.

Hexidecimal numbers:

(base 16) are written with "h" following the number: 0Fh=15.

ICM:

Incom Communication Module. The software driver module used to handle the protocol of the CONI card from the application software.

I/O:

Input Output.

Input:

The direction is always to the IBM PC unless otherwise indicated.

K:

when referring to size, it represents 1024.

LSB:

Least Significant Bit.

MSB:

Most Significant bit.

nibble:

A four bit word. Typically 1/2 byte.

output:

the direction is always from the IBM PC unless otherwise indicated.

PR0M:

Programmable Read Only Memory

RAM:

Random Access Memory.

Rx:

Receiver.

String:

A sequence of characters.

Tx:

Transmitter.

The system disk, with DOS Ver. 2.10 or greater on it, used to boot up the computer, must have a file called CONFIG.SYS with DEVICE=INCOM.COM in it. This file is loaded into the computer at boot time and loads the ICM device driver (INCOM.COM) which becomes part of the operating system. INCOM.COM must also be peasant on the same disk.

The CONI card installed in the IBM PC must be strapped to generate an interrupt request #3, as described in detail heretofore. This corresponds to interrupt vector number 0Bh in the operating system. The ICM modifies and utilizes system interrupt vector numbers 0Bh (unused by DOS-hardware interrupt #3) and lCh (Timer Tick). The ICM adds 2270 bytes to the operating system.

The ICM allows the sending or receiving of commands or data information to and from the INCOM network through the CONI card. It also allows the sending of control information to the CONI card to change the master address or set baud rates, as described in detail heretofore. The commands, data or control information is sent via an eight byte string to the ICM. The input data is retrieved in a four byte string from the ICM.

The ICM will buffer thirty-two (32) output commands, data or control messages (eight bytes each) and thirty-two (32) input messages (four bytes each). If more than thirty-two messages are received before the first message is retrieved by the application software, the last message received will be lost. If more than thirty-two commands, data or control information messages are sent, the ICM will return a busy to the calling program.

The TX or output message is an eight (8) byte string having the following format:

1st byte--This byte is the control byte. If this byte is a binary zero (0000 0000b), this indicates the following bytes are data to be sent to the INCOM network and a "0" will be put in control bit (22) of the INCOM data message (FIG. 11). If this byte is a binary one (0000 0001b), this indicates the following bytes are a command to the INCO network and a "1" will be put in bit (B2) of the INCOM command message, as shown in FIG. 11. If this byte is a binary two (0000 0010b), it indicates that this message is a control message to change the master address and that the next two bytes are the address desired. If this byte is a binary three (0000 0011b), this indicates that this message is a control message to change the baud rate of the INCOM network and the next byte is the baud rate desired. If this byte is a binary four (0000 0100b), it indicates that this message is a control message to reset the receive timeout timer of the ICM.

2nd byte--If the 1st byte is zero, then this 2nd byte is the first data byte to be sent to the INCOM network. This data will be put into bits B3 through B10 in the INCOM message with the LSB in B3 and MSB in B10.

If the 1st byte is one, then the least significant nibble of this 2nd byte is the four bit instruction to be sen to the INCOM network. The most significant nibble of this 2nd byte will be ignored. The least significant four bit nibble will be put into bits B3 through B6 of the INCOM command word with the LSB in B3 and bit 3 of the byte in B6, as shown in FIG. 11.

If the 1st byte is two, then this 2nd byte is the least significant byte of the new master address. This will be sent to the address register 76 of the CONI card at 40 address 304h to change the address of the master, as described in detail heretofore.

If the 1st byte is three, then this 2nd byte is the new baud rate desired for the INCOM network which is sent to the CONI card at I/O address 308h of the control register 70, as described in detail heretofore. The ICM initializes at 1200 baud. The baud rates can be change by setting this 2nd byte to the following values:

0000 0000b=no change--leaves baud rate at last rate set.

0000 0001b=38.4 KHZ

0000 0010b=1200 baud

0000 0011b=300 baud

If the first byte is four, this 2nd byte is ignored. This 2nd byte must still be present in the eight byte string.

3rd byte--If the 1st byte is zero, then this 3rd byte is the second data byte to be sent to the INCOM network. This data will be put into bits B11 through B18 in the INCOM data message with the LSB in B11 and the MSB in B18.

If the 1st byte is one, then the least significant nibble of this 3rd byte is the four bit command to be sent to the INCOM network. The most significant nibble of this 3rd byte will be ignored. The leas significant four bit nibble will be put into bits B7 through B1.0. of the INCOM command word with the LSB in B7 and bit 3

of the byte in B10, as shown in FIG. 11. If the 1st byte is two, then the low nibble of this 3rd byte is the high nibble of the new master address desired. The low nibble of this 3rd byte will be sent to the address register 78 of the CONI card at I/O address 30Ah to change the master address, as described in detail heretofore.

If the 1st byte is three or four, this 3rd byte is ignored. This 3rd byte must still be present in the eight byte string.

4the byte--If the 1st byte is zero, then this 4the byte is the third data byte to be sent to the INCOM network. This data will be put into bits B19 through B26 in the INCOM message with the LSB in B19 and the MSB in B26.

If the 1st byte is one, then this 4the byte is the least significant eight bits of the address field of the INCOM command word. This 4the byte will be put in bits B11 through B18 in the INCOM command word with the LSB in B11 and MSB in B18, as shown in FIG. 11.

If the 1st byte is either two, three or four, this 4the byte is ignored. This 4the byte must still be present in the eight byte string.

5the byte--If the 1st byte is zero, two, three or four, this 5the byte is ignored. This 5the byte must still be present in the eight byte string.

If the 1st byte is one, then the least significant nibble of this 5the byte is the most significant nibble of the address field of the INCOM command word The most significant nibble of the 5the byte is ignored. The least significant nibble of this 5the byte is then put into B19 through B22 of the INCOM command word with the LSB in B19 and the MSB in B22, as shown in FIG. 1.

6the byte--If the 1st byte is zero, two, three or four, this 6the byte is ignored. This 6the byte must still be present in the eight byte string.

If the 1st byte is one, then the least significant nibble of this 6the byte is the application command or data to be put in the INCOM command word. The most significant nibble of this 6the byte is the number of retries minus one. The least significant nibble of this 6the byte is put into bits B23 through B26 of the INCOM command word with the LSB in B23 and the MSB in B26, as shown in FIG. 11.

7th byte--If the 1st byte is zero or one, this 7the byte is the operation code used by the ICM to att on the previous data passed to it. The bit positions of the 7the byte are described as follows:

bit 0

This bit tells ICM if there is a response expected. A one in this bit means a response is expected. A zero in this bit means no response is expected.

* bit 1

This bit tells ICM that it should wait an interval equal to the binary value of the 8the byte times 55 milliseconds for a response and then flag an error or retry the command. If tis bit is a one then the 8the byte is utilized to compute time delay. If this bit is a zero then the 8the byte is ignored. If this bit is zero, the number of response messages expected back is set to zero regardless of bit 0 being set to one.

* bit 2

This bit tells ICM to retry the command after the time out interval. The number of retries is set by bits 4 through 7 of the 6the byte. If this bit is a one then the ICM will retry the command the number of times set forth in bits 4 through 7 of the 6the byte after waiting the full timeout interval for each retry. If this bit is a zero then no retries will take place. Retries are only allowed with command messages which require one response message. Therefore, if the 1st byte is not zero or more than one response message is expected, this bit is ignored. If bit 1 is zero, retries are set to zero regardless of this bit being one.

*bit 3 through bit 7

If bit .0.=one, then bit 3 through bit 7 is the number of messages expected back from the INCOM network. The maximum number is 32 (Rx buffer size). Bit 7 is the MSB and bit 3 is the LSB of the number of messages. If bits 3 through 7 are greater than 32, then ICM forces the messages expected to 32.

*If bit 0=zero, then the bits with an asterisk are ignored.

If the 1st byte is two, three or four, this 7the byte is ignored. This 7the byte must still be present in the eight byte string.

8the byte--This byte is the time delay.times.55 milliseconds for the ICM to wait before retrying or erroring out. The range is from 1 to 254.times.55 msec. or approximately 14 seconds max. This byte is ignored if bit 0 or bit 1 in the 7the byte is a zero. If bit 0 and bit 1 of the 7the byte are one and this 8the byte is zero, ICM forces zero retries. If this 8the byte is 255 (FFh or 1111 1111b), this indicates a wait delay of indefinite duration. The only way to clear the transmitter after giving this delay is to issue an RX TIMER RESET command (1st byte=four). The reason for this option is to allow the application software to control the timeout delay (i.e. to provide timeout delays greater than fourteen seconds).

The RX or received (input) message is a four (4) byte string having the following format:

1st byte--This byte is data bits B3 through B10 of the received message, as shown in FIG. 12.

2nd byte--This byte is data bits B11 through B18 of the received message, as shown in FIG. 12.

3rd byte--This byte is data bits B19 through B26 of the received message, as shown in FIG. 12.

4byte--This byte is the status byte of the received message which is developed by the ICM and supplied to the IBM application software. The bits of the 4the byte have the following meaning:

* bit 0

If this bit is a one (1) then the preceding bytes are valid. If this bit is a zero, then the preceding data is not valid. Such a situation can arise, for example, when the IBM application software reads from the ICM RX buffer when no message has been received from the INCOM network by way of the CONI card.

* bit 1

When this bit is a one (1), then this means that all messages from the last transmission have been received and are in the Rx buffer. This bit will be set in the last message received.

* bit 2

When this bit is a one (1), this means that more than thirty-two (32) messages have been received and the last message is lost.

* bit 3

If this is a one (1), this means that a timeout error on the received messages has occurred.

* bits 4 and 5

These bits are undefined

* bit 6

This bit is set if the received message was received with a BCH error and corresponds to bit "ber" of the receive buffer 50 on the CONI card, as shown in FIG. 12

* bit 7

This bit corresponds to bit b2 of the INCOM message on the receive buffer 50 on the CONI card, as shown in FIG. 12. If this bit is a zero, the previous bytes are data from the INCOM network If this bit is a one, the previous bytes are a command from the INCOM network.

There are two error codes that ICM can return to DOS. They are: UNKNOWN COMMAND (DOS error code 03) and DEVICE NOT READY (DOS error code 02). The error codes are described as follows:

* UNKNOWN COMMAND

This code is returned if all eight (8) TX message bytes are not received by ICM from the application software within two (2) seconds after the first byte is transferred to the ICM. This error code will be returned the next time a TX message is sent to ICM by the application software.

* DEVICE NOT READY

This code is returned if the TX que buffer of the ICM has thirty-two (32) messages in it and is full. ICM then waits then (10) seconds for the que buffer to become free to take another message. If at the end of the ten second timeout the Tx buffer has not become free to take another message, then ICM returns this error code to DOS. From the foregoing detailed description of the operating disciplines of the ICM, the listing in Appendix B and the flow charts shown in FIGS. 15-21, inclusive, it will be seen that the ICM stores the eight byte output string from the IBM application software and assembles a command or data message conforming to the protocol of the INCOM network, such as the command message to a stand alone slave or enabled mode slave on the INCOM network shown in FIG. 11, and writes it into the transmit buffer 40 of the CONI card. The ICM also sends control messages to the control register 70 of the CONI card at I/O address 308h, as shown in FIG. 13.

Considering in more detail the operation of the ICM in response to an eight byte output string, the lst or control byte is decoded to determine whether the remaining bytes of the string comprise information relating to a command, data or control message. If the lst byte is a binary "1" (0000 0001b) the ICM interprets the succeeding bytes as relating to an INCOM command message and assembles the portions thereof described below into a command message having the format shown in FIG. 11 in which the first or control bit B2 is a "1":

2nd byte--least significant nibble is bits B3-B6 of INCOM command message.

3rd byte--least significant nibble is bits B7-B10 of INCOM command message.

4the byte--least significant eight bits B18) of INCOM slave address.

5th byte--least significant nibble is most significant 4 bits (B19-22) of INCOM slave

6th byte--least significant nibble is the application command bits (B23-26) of the INCOM command message. The most significant nibble of the 4th byte indicates the mumber of times (-1) that the ICM is to retry sending tee INCOM command message in the event it does not receive a reply from the addressed slave within a timeout interval determined by the decoded value of the 8th byte in the string.

7th byte--This byte is decoded as the operation code described in detail heretofore. If bit 0 is a one, indicating that a response is expected, the ICM stores bits 3-7 as the number of messages expected back from the INCOM network.

8th byte--If one or more retries are to be made, the ICM uses this byte to determine a timeout interval (decoded value of this byte .times.55 milliseconds) which it will wait before retrying (sending the same INCOM command message to the CONI card and waiting for a reply) or erroring out.

If the 1st or control byte of the eight byte string is a binary "0" (0000 0000b) the ICM interprets the succeeding bytes as relating to an INCOM data message to an enabled mode slave previously addressed and assembles the portions thereof described below into a data message in which the control bit B2 is "0 ":

2nd byte--data bits B3-B10 of the INCOM data message

3rd byte--data bits B11-18 of data message

4th byte--data bits B19-26 of data message

5th byte--ignored

6th byte--least significant nibble is ignored. Most significant nibble indicates number of retries (-1) in the event no reply is received from the enabled mode slave.

7th byte--This byte is decoded as the operation code described in detail heretofore.

8th byte--This byte is used to determine the timeout interval, as described above in connection with an INCOM command message.

If the 1st or control byte of the eight byte string is a binary "2" (0000 0010b) the ICM interprets the succeeding bytes as relating to a control message to the master address registers 76, 78 on the CONI card and assembles the portions thereof the data bus 28 and I/O addresses 309h and 30Ah on the address bus 26 are employed to write into the registers 776, 78 as described in detail heretofore:

2nd byte--least significant byte of master address (register 76)

3rd byte--least significant nibble is most significant nibble of master address (register 78)

4th byte--ignored

5th byte--ignored

6th byte--ignored

7th byte--ignored

8th byte--ignored

If the 1st byte of the eight byte string in a binary "3" (0000 0011b) the ICM interprets the succeeding bytes as relating to a control message to the control register 70 on the CONI card to change the baud rate of the INCOM network and assembles the portions thereof described below into a baud rate control message which is written into the control register 70 at I/O address 308h, as shown in FIG. 13:

2nd byte--The two most significant bits of this byte are the new baud rate (B6 and B7 in FIG. 13).

3rd to 8the bytes--ignored

The ICM also writes an initiate transmit (Tx) bit in B0 of the control register 70 after a command or data message has been written into the transmit buffer 40 or an acknowledge receive (Rx) bit in B1 of the control register 70 after a received message has been read from the receive buffer 50 on the CONI card, as described in detail heretofore.

If the 1st byte of the eight byte string is a binary "4" (0000 0100b) the ICM responds thereto by resetting its own internal timer and ignores the remaining bytes of the eight byte string. It will be recalled from the preceding description of the 7th byte operation code that the ICM responds to a timeout value of 255 in the 8th byte of the string by disabling its internal timer so that a wait delay of indefinite duration is initiated. The RX TIMER RESET command (1st byte=4) may then be used by the application software when delays greater than fourteen seconds are needed.

As discussed generally heretofore, when a number of messages are to be received back from the enabled slave on the INCOM network the ICM stores bits 3-7 of the 7th byte of the TX string and counts the number of messages received back from the INCOM network. When the number of messages stored in the ICM receive buffer equals the stored bits 3-7, the ICM sets bit 1 of the 4th byte (status) in the last received message to inform the application software that all messages in response to the last transmission have been received.

If the RX buffer of the ICM overflows, bit 2 of the 4th status byte of the next received message read from the RX buffer will be set to indicate to the application software that more than thirty-two messages have been received and the last message has been lost.

Referring now to the flow charts for the ICM driver module, FIG. 15 is an overall flow chart illustrating how the ICM functions with the timer task interrupt service routine of the IBM PC DOS operating system which generates an interrupt signal every 55 milliseconds. FIG. 16 is a flow chart of the ICM timer tick routine which uses the DOS system timer tick to determine whether all eight bytes of the eight byte output message string have been developed by the application software within a predetermined time interval This figure also shows how the ICM utilizes the DOS system timer tick to establish a receive timeout interval during which a response to the output message of the master should be received from the INCOM network.

FIG. 17 is a flow chart illustrating how the ICM responds to a CONI card interrupt. If an INCOM message has been received by the CONI card, the ICM stores the message, as shown by the GET Rx MESSAGE routine of FIG. 18. It will be noted from FIG. 18 that the ICM releases the CONI card and sets an overflow error if the number of messages from the CONI card is greater than the capacity of the Rx buffer of the ICM, i.e., greater than 32 response messages. The ICM also increments its response messages received counter as each response message is received and when the number of messages received equals the number of responses expected (bits 3 through 7 of 7th byte of the eight byte string) the ICM sets an all response messages received flag (bit 1 of 4th byte of last Rx message) to inform the application software of this event.

From FIG. 17 it can also be seen that if all messages have been received from the CONI card, no messages are comings in from the CONI card and it is ready to take another message, the process command routine shown in FIG. 19 is utilized. Referring to FIG. 19, it will be seen that the ICM determines whether a command from the application software is stored in its que buffer and whether this command is a control message (baud rate or counter address change) or a command or data message. If it is a data message, the data is sent to the CONI card, the number of retries is set to zero and the number of return messages is initialized to zero. If a response is expected back (bit 0 of 7th byte) the number of responses is determined from bits 3 through 7 of the 7th byte. If the application software attempts to call for more response messages than the ICM is capable of handling, the ICM forces the number of responses to the maximum allowed and then stops transmitting any further output messages until all bytes of the expected response messages have been received.

If the eight byte string is a command message to the INCOM network, the ICM reformats the control bit, INCOM instruction, INCOM address and master command derived from the eight byte string into the format required by the INCOM network and sends the command to the CONI card. The number of responses and number of retries are determined from the eight byte string as well as the desired setting for the timeout timer and an initiate transmit (INIXMT) is then sent to the CONl card.

FIG. 20 is a flow chart of the operation of the ICM in receiving an eight byte string from the DOS operating system of the IBM and FIG. 21 is a flow chart of the operation of the ICM in inputting data to the DOS operating system upon request.

While there has been illustrated and described a single embodiment of the present invention, it will become apparent that various changes and modifications thereof will occur to those skilled in the art. It is intended in the appended claims to cover all such changes and modifications as fall within true spirit and scope of the present invention. ##SPC1##