Selective Call Receiver With an Intelligent Memory System

The present invention concerns local call systems and, more specifically, the memorization and manipulation of message information received by a local call receiver. In what follows in the present description such local call receivers will be designated by the word "pager" this term now being very largely admitted and employed as much by specialists as by the public which makes use of such receivers.

The present invention may be used in portable pagers adapted to receive message signals broadcast at high frequency, the invention being described hereinafter in relationship with this example of application to which, however, it is not limited.

Telecommunication systems in general and pager systems more specifically using radio broadcast message signals are presently largely employed so as to assure calling of pagers with the purpose of sending them information selectively from a central station. Such information is transmitted by means of coding schemes and predetermined message formats, such as those known under the terms POCSAG or GOLAY. In respect of the scheme POCSAG, reference may be had to the recommendation of the CCIR 584-1, Dubrovnik, 1986.

The predominant transmission coding schemes used for calling pagers have evolved from simple systems based on sequential acoustic signals towards formats based on code words made up of numerous bits and the functions offered to the user have changed in a corresponding manner from a simple acoustic warning signal to a complex multifunctional alert requiring reading of numeric or alphanumeric data on a display.

To obtain such multifunctional possibilities, pager systems and present pager-receivers include microprocessors or even microcomputers enabling them to react to information containing a large variety of coded radio-broadcast message signals. To this end known pagers are capable of receiving such signals, demodulating them, extracting therefrom dedicated call signal information and message information as such, memorizing such information and finally displaying certain selected elements of the message as transmitted.

Prior art pagers also permit the user to have at his disposition special functional possibilities such as the later repetition of messages already received and the display of the number of messages received or the time of day.

The microcomputers employed in known pagers are designed to control the operation of the receiver in order that the latter may receive radio-broadcast message signals and in order to accomplish the decoding functions of the coded message signals, memorization of given message signals, control of the display and manipulation of stored message signals in order that the various user controllable functions may be performed.

One of the major requirements of a pager is that it must handle information received in real time, otherwise there will be a risk of loss of information, for example by reason of the fact that the decoding speed is too low relative to that at which the information is received. Consequently, the operations performed by the microcomputer relative to reception, decoding, memorization and manipulation of received coded message information must be sufficiently rapid in order that the results obtained are useful for controlling the arrangement without risking loss of information. One thus must use particularly high performance microcomputers operating at a high speed.

The clock frequency necessary to attain the high operational speeds in real time can be for instance 500 kHz. Such high clock frequencies increase the feed voltage and energy consumed by the pager whilst rendering it more expensive. At the present the battery necessary for energizing current microcomputers determines to a large extent the cost, dimensions and the weight of pagers.

Additionally, such high clock frequencies and the signals which they induce in the circuits of the pager at harmonic frequencies of the clock frequency seriously disturb the processing quality which is to be expected in a good pager. Furthermore, the high consumption of energy and the physical limits of such microcomputers also bring about a limitation of functions which can be performed and offered in existing pagers.

It is also current practice to repeat two or three times the diffusion of message signals in order to guarantee that the pager for which such signals are intended receives them correctly. Known pagers thus include memory space the dimensions of which must be compatible with memorization not only of the original message signals, but also of their repetitions. The additional memory capacity which is necessitated by such repetitions increases still further the energy consumption and the cost of known pagers.

The purpose of the invention consists in providing a pager which limits or even eliminates the disadvantages of prior art pagers.

The invention thus has as its objective a pager intended to receive radio-broadcast message signals comprising call signal information and message information, said message information comprising one or several messages, said pager comprising a receiver intended to receive and to demodulate coded message signals, a memory arrangement for storing said message information, a decoder intended to decode such coded message signals and for selectively furnishing said message information to said memory arrangement, function control means capable of furnishing control signals to said memory arrangement and receiving therefrom message information which is stored therein, said pager being characterized in that said memory arrangement comprises internal processing means in order to control the reception of message information coming from said decoder.

Thus, the selected message information furnished by the decoder may be memorized by the memory arrangement without it being necessary to have instructions available from a microcomputer or a microprocessor outside such memory, this latter becoming thus in a manner of speaking "intelligent".

As a result, the selected message information may be directly memorized in real time in the intelligent memory arrangement which enables the microcomputer or microprocessor external to said memory means to accomplish other pager functions without the clock frequencies or processing speed being as high as in known pagers.

According to another characteristic of the invention, the pager may also be adapted in order to assure manipulation of stored message information in the memory arrangement so that deletion, copying and shifting of information thus memorized may be brought about within the memory arrangement, removing thus the limits imposed by such operation to the function control means, otherwise referred to as the pager microcomputer.

According to a still further characteristic of the invention, the pager may also be made capable of comparing message information received by the memory arrangement with previously stored information. In this manner, it is sufficient to memorize only the message information which differs from the message information previously stored, this reducing the required storage capacity.

Other characteristics and advantages of the invention will appear in the course of the following description which is given solely by way of example and drawn up with reference to the attached drawings.

FIG. 1 is a simplified schematic of an embodiment of a pager in accordance with the invention;

FIG. 2 is a diagram representing the POCSAG coding scheme which is used to transmit message information intended for the pager of FIG. 1;

FIG. 3 is a more detailed schematic of the pager according to the invention;

FIG. 4 is a simplified schematic of a memory arrangement used in the pager of FIG. 1 and

FIG. 5 schematically shows a read-write memory (RAM) employed in the memory arrangement of FIG. 4.

Referring now to FIG. 1 of the drawings, there is shown a simplified functional block diagram of pager 1 constructed in accordance with the present invention. The pager 1 comprises an antenna 2, and a receiver 3 connected to the antenna 2, for receiving transmitted coded message signals from a central station or other source from which it is desired to call the user of the pager 1. The transmitted coded message signals may contain selective call signalling information, identifying a particular one of several pagers of the type shown in FIG. 1, and chosen message information, and may be in the POCSAG or other suitable coding scheme format. The transmitted coded message signals detected at the antenna 2 are demodulated by the receiver 3 and a serial stream of binary data representing these coded message signals is provided at an output 3a of the receiver 3.

The pager 1 also comprises a decoder 4 connected to the output 3a of the receiver 3 at its input 4a. The decoder 4 contains a memory area 4d for storing certain predetermined address information to which the pager 1 will respond. The decoder 4 is adapted so that a comparison is made between the coded message signals received at its input 4a and the predetermined address information stored in the memory area 4d. If the selective call signalling information matches one of the stored addresses, the decoder provides the message information associated with the coded message signals at its output 4c.

The pager 1 further comprises an intelligent memory device 5 connected to the output 4c of the decoder 4 at its input 5a. The intelligent memory device 5 includes a data processing unit 6 and a memory area 7. The intelligent memory device 5 is adapted to receive the selected message signals provided at its input 5a and store these message signals in the memory area 7. The data processing unit 6 is adapted to control the manner in which these message signals are stored in and retrieved from the memory area 7, and perform associated manipulations of the message signals, addresses, stack pointers and other internal variables. The detailed functioning of the intelligent memory device 5 will be explained later.

The pager 1 additionally comprises a microcomputer 8 connected to the output 5c of the intelligent memory 5 at its input 8a. The microcomputer 8 includes in a known manner a display interface 9, a microprocessor 10, a random-access memory (RAM) area 11 and a read-only-memory (ROM) area 12. The display interface 9 is adapted to display chosen message information by driving a display 13 via an input 13a, and includes a serial driver circuit and serial multiplexed liquid crystal (LCD) driver circuits. The display 13 comprises an LCD display suitable for displaying the message information stored in the memory area 7 of the intelligent memory 5, and may also be adapted to display time or other information.

The ROM area 12 contains firmware for controlling the operation of the microprocessor 10, such as programs for the display of the indicia corresponding to the message information stored in the memory area 7, for controlling the input and output functions of the microcomputer 8, for providing command signals to the intelligent memory 5 and the decoder 4, and for controlling the basic system timing of the microcomputer 8. The RAM area 11 is used for temporary data storage within the microcomputer 8, and amongst other functions provides a data buffer for message information provided from the intelligent memory 5 which is to be displayed.

The pager 1 further comprises an input control circuit 14 for providing data, at an output 14a to an input 8b of the microcomputer 8, indicative of input information provided by a user. User inputs 14b, c, d and e are connected to the input control circuit 14 and may be in the form of pushbuttons, rotatable buttons or other actuable members in order that a user can control some of the operations of the pager 1. The input control circuit 14 may also be adapted to control other devices associated with the pager 1. For example a timepiece may be combined with the pager 1 and the user inputs 14b, c, d and e may be used to provide user control of some of the functions of the timepiece. In addition, the input control circuit 14 may directly control the operation of some of the functions of the timepiece associated with the pager 1, such as providing current to energise the motor 15 of an electronic watch movement. It is to be noted that the pager thus combined with a timepiece may take the form of a wrist-watch.

A portable power supply 16, which may be a battery, is also provided in the pager 1 for supplying power to the input 3b of the receiver 3, the input 4b of the decoder 4, the input 5b of the intelligent memory 5 and the input 8c of the microcomputer 8, from its output 16a. Another portable power supply 17 having an output 17a is provided to supply the input control circuit 14 with power at its input 14f. This arrangement advantageously supplies power from separate sources to the pager 1 and any associated devices, such as a timepiece, so that in the event that, for example, the battery supplying the pager becomes discharged, the timepiece may continue to function. It is to be appreciated however that both the pager 1 and any associated devices may be supplied from a single power source.

An example of the message information and pager coding scheme used for transmitting message signals such as those used by pager 1 is shown in FIG. 2. The system POCSAG, well known to specialists in the art, uses a digital coding format made up from groups of code words 20, themselves each made up of a synchronization word 21 and a group 22 of eight frames each consisting of two code words, such groups of code words being transmitted in a serial format at regular intervals. Each group 22 of eight frames is transmitted following a synchronization word 21, the eight distinct frames being adapted to contain address information and message information. For purposes of explanation the lower portion shows in detail a single group of code words 20. Each frame including an address-code word, 23.1 to 23.8 respectively, and a message code word 24.1 to 24.8 respectively.

Thus, in the example shown in FIG. 2, each pager of a group formed of pagers in conformity with that shown in FIG. 1, must operate on one of the eight address-code words in a manner such that each of such words represents the call signalling information with the help of which each pager of the group is respectively identified.

The invention will be better understood in referring to FIG. 3 which shows a more detailed schematic of a preferred embodiment of pager 1 according to the invention. As already described hereinabove, pager 1 basically comprises an antenna (not shown on FIG. 3), receiver 3, decoder 4, intelligent memory 5 and microcomputer 8. The circuit 14 for control inputs intended for controlling a timepiece 15 associated with the pager is also shown on FIG. 3.

Receiver 3 is connected by terminal 3.1 to a positive supply line 16.1 of the portable power supply 16 (not shown on FIG. 3), its negative terminal 3.2 being connected to a negative supply line 16.2 of the power supply 16. In a known manner, radio broadcast coded message signals are captured and demodulated by receiver 3 and the antenna to which the latter is connected so that groups of binary data such as those shown in FIG. 2 are generated at the output 3.3 of receiver 3 and transmitted to the input 4.1 of decoder 4. Receiver 3 includes in its internal circuitry an assembly (not shown on the figures but known per se) for checking the voltage of the energy source 16, such assembly providing a signal indicating low voltage of such source on output 3.4 of receiver 3. The output 3.4 transmits in such case the low voltage indication signal to other circuits of pager I in order that a display readable by the user may be assured on the display 13.

Decoder 4 is connected to the positive supply line 16.1 by its terminal 4.4 and to the negative supply line 16.2 by its terminal 4.5. A voltage stabilization capacitor 4d is connected between terminals 4.4 and 4.5. The decoder may be of the type PCA 5001 manufactured by Philips and its task is to separate the selective call signal information from the message information as such in the coded message signals and to compare the call signal information with the predetermined address information stored in the decoder and individual to the pager under consideration.

If the collective call signal information corresponds to one of the stored addresses, every message code word following the address code considered up to the following address code word is transmitted in the form of serial data from the output 4.6 to the input 5.1 of the intelligent memory 5.

The output 4.7 from the decoder 4 furnishes a data transfer signal in order to permit reading by the intelligent memory 5 of data available at the output 4.6, such signal assuming a high level or a low level at the input 5.2 of memory 5. The message information furnished to output 4.6 is introduced into the storage area 7 of the intelligent memory 5 when a complete data byte has been transferred from receiver 3 to decoder 4.

A resonator circuit 25 is connected to the decoder 4 through inputs 4.8 and 4.9 of this latter. It comprises basically a quartz resonator 25a connected in parallel to a damping resistor 25b and to the inputs 4.8 and 4.9. The positive supply line 16.1 is connected to one of the quartz resonator terminals 25a through a resonance capacitor 25c. The resonator circuit 25 cooperates with the internal circuitry of decoder 4 in order to form an oscillator circuit which furnishes a periodic wave form of 32 kHz for example to decoder 4 in order to determine the rate of transmission of message signals from receiver 3 towards decoder 4. As is well understood, other clock frequencies may be used as a function of the transmission rate of message signals. The resonator circuit 25 is also used to furnish a clock signal to the microcomputer 8 and to the intelligent memory 5. Such clock signal is furnished to the microcomputer 8 via the output 4.10 of decoder 4. The values of the resistor 25b and of the capacitor 25c may respectively be 4.7M .OMEGA. and 10 pF.

Decoder 4 comprises a reprogrammable electrically erasable memory of the EEPROM type (not shown) in which are stored the system parameters of the decoder 4. Control signals can be sent from the microcomputer 8 towards the inputs 4.11, 4.12 and 4.13 in order to control the functions of the decoder 4. One of the functions of the decoder 4 which may be controlled is the rate of bit transmission between decoder 4 and the intelligent memory 5, such rate going as high as 5000 bits/second. In such case, the message information is stored in the circular buffer located in the intelligent memory 5 without undergoing any other processing (such as comparison between the last two messages which have just been stored).

The input 5.3 of intelligent memory 5 is connected to the positive power supply line 16.1 while the input 5.13 is coupled to the negative line 16.2. The time base for the intelligent memory 5 is determined by the clock signal furnished by output 8.8 of the microcomputer 8 to the input 5.4.

The intelligent memory 5 shows four terminals 5.5, 5.6, 5.7 and 5.8 respectively connected to corresponding terminals 8.1, 8.2, 8.3 and 8.4 of the microcomputer 8, which assures a simple parallel connection with this latter enabling the sending of control signals from the microcomputer 8 to the intelligent memory 5 and the sending back of message information stored in memory area 7 of intelligent memory 5 towards the microcomputer 8 in order that such message information can be displayed. Depending on the nature of the control signal which is transmitted terminals 5.5 to 5.8 may also control the intelligent memory 5 in order to furnish the microcomputer 8 with status information in respect of the reception of message information by memory 5. Other control signals may control the latter in order that it manipulates message information which is stored therein as will subsequently appear herein. A data transfer input 5.11 for memory 5 is also provided in order to assure the simultaneous transfer of data towards terminals 5.5 to 5.8.

An input 5.9 determines whether inputs 5.5 to 5.8 carry data or introduce control signals into the intelligent memory 5. When a high level signal is present on input 5.9, the signals on inputs 5.5 to 5.8 are interpreted as being control signals coming from the microcomputer 8, while if a low level signal is present, the signals are interpreted as constituting data.

A terminal 5.10 of intelligent memory 5 enables informing the microcomputer 8 that the memory is ready to receive control signals. A high level logic signal on terminal 5.10 is interpreted by the microcomputer 8 as indicating that memory 5 is ready for a further communication with the microcomputer 8 while a low level logic signal is interpreted as signifying that memory 5 is still in the process either of accomplishing a manipulation on the data or another operation, or is transferring data to the microcomputer 8.

An output terminal 5.12 from memory 5 serves to provide an interrupt signal to the microcomputer 8 in order to indicate thereto its functional status in response to the received message information or to the control signals. A high level logic signal is sent to the microcomputer 8 if, for example, fresh or repeated message information is received or if an unknown, forbidden or unperformable function is required by the microcomputer. Such interrupt signal may thus be used in order to indicate to microcomputer 8 that a new operation is required, such as for instance to announce the arrival of fresh message information or the sending of a new instruction to the intelligent memory 5. A low level signal indicates that no new action is required by the microcomputer 8.

Such microcomputer 8 may be of a known type suitably programmed. It is connected to the positive supply line 16.1 by its input 8.5 and to the negative supply line by its input 8.6. An input 8.7 receives the clock pulse train from the output 4.10 of decoder 4. An output terminal 8.8 furnishes a clock signal to the input 5.4 of the intelligent memory 5.

Microcomputer 8 also comprises output terminals 8.9 and 8.11 in order to furnish control signals and to transfer data as described hereinabove respectively to inputs 5.9 and 5.11 of the intelligent memory 5, while input terminals 8.10 and 8.12 are provided in order to receive respectively the acceptance and interrupt signals of the intelligent memory 5 as described hereinabove.

A liquid crystal display 13 is connected to microcomputer 8. It comprises segments numbered from 00 to 47 which are connected to the display driver circuit (not shown on FIG. 3) of microcomputer 8 by a bus 13a such that each segment may individually be controlled and that the desired message information may be displayed by display 13. Specialists in the art will understand that various voltage values are necessary for the driver circuit in order to control the various segments of the display 13. Input terminals 8.13 to 8.16 are connected to the positive supply line 16.1 through capacitors 8d to 8g in order to provide these various voltages. Capacitors 8d to 8g may have respective values of 220, 100, 100 and 100 nF. Microcomputer 8 also comprises output terminals 8.17, 8.18 and 8.19 in order to furnish, in a known manner, control and time base signals to the display 13 coming from the driver circuit.

The input terminals 8.20, 8.21 and 8.22 are provided in order to stabilize and smoothe the internal voltage levels of the microcomputer 8. One of the terminals of a capacitor 8h is connected to the input 8.20 while one of the terminals of another capacitor 8i is connected to the input 8.21. The other terminals of capacitors 8h and 8i are connected together to terminal 8.22.

The microcomputer 8 is also provided with user control inputs 8.23 to 8.26, each one of which is connected to the positive supply line 16.1 through switches 8j, 8k, 8l and 8m which may be actuated by the user. When this occurs, a high level logic signal is applied to the control inputs by the user, for instance when he wishes to put the pager 1 into or out of operation, render it silent, protect the message displayed by display 13 or delete a displayed message as will be explained hereinafter. It will be understood that various other user control functions may be provided in this manner and that a separate input is not necessary for each of such functions thus provided; for example one or several switches or push-buttons can be actuated according to a special sequence in order to indicate to microcomputer 8 that a certain function is to be performed.

The circuit 14 for control inputs and the timepiece is connected to the positive supply line 17.1 from the portable energy source 17 (not shown on FIG. 3) by terminal 14.1 and to the negative supply line 17.2 from supply 17 by terminal 14.2.

Circuit 14 also comprises inputs 14.3. 14.4 and 14.5 which serve to form supplementary user inputs in order to enable the pager 1 to perform certain functions ordered by the user and also to control the operation of the timepiece 15 which is controlled by circuit 14. A special sequence of signals applied to inputs 14.3, 14.4 and 14.5 or signals initially sent to other inputs may be used in order to determine whether inputs 14.3, 14.4 and 14.5 control the operation of the pager or the timepiece 15. Inputs 14.3, 14.4 and 14.5 are respectively connected to one of the terminals of switches 14b, 14c and 14d, their other terminals being connected together at input 14.1. The switches may be provided under any form usable by the user. Another switch 14e is connected between the positive supply line 17.1 and an input 8.27 of the microcomputer 8 in order to indicate thereto whether it is the pager or the timepiece which is being controlled.

Circuit 14 further includes two outputs 14.6 and 14.8 respectively connected to one of the terminals of the two windings 15a and 15b of the timepiece 15. The other terminals of such windings are connected to a common return connection 14.7. Those skilled in the art will understand that in the example chosen herein windings 15a and 15b belong to a bidirectional motor of an analog quartz time-piece well known moreover, but that any other type of time-piece may be provided, including a digital timepiece in which case, as is well understood, a watch motor is not necessary. Various other inputs may be provided for circuit 14 in order to control any other function of the timepiece.

Two other outputs 14.9 and 14.10 of circuit 14 are respectively coupled to inputs 8.28 and 8.29 in order to furnish the microcomputer 8 with data representing the signals applied to inputs 14.3, 14.4 and 14.5. A quartz resonator 14.9 is coupled to input 14.11 and to output 14.12 of circuit 14 in order to constitute a timebase for the latter.

Pager 1 also comprises a warning device 26 coupled to the microcomputer 8 in order that new message information received by decoder 4 may be announced. An electrical acoustic transducer 26a (buzzer) is connected by one of its terminals to the collector of a switching transistor 26b and by its other terminal to the positive supply line 16.1. The collector of transistor 26b is also connected to the output 8.31 of the microcomputer 8 through a polarization resistor 26c which may have a value of 18 k.OMEGA.. Normally, this output is maintained at a high logic level. The emitter of transistor 26b is connected to the negative supply line 16.2 and to terminal 8.6 of the microcomputer 8. The base of transistor 26b is connected to the output 8.30 of the latter. A choke 26d having an inductance of 45 mH, for instance, is connected in parallel with the buzzer 26a. Finally, a voltage stabilizing capacitor 26e having a value of 4.7 .mu.F, is connected between the positive 16.1 and negative 16.2 supply lines. In normal operation, the output 8.30 is maintained at a low level and transistor 26b is non-conducting.

When pager 1 is to announce reception of a call or the accomplishment of another function, a signal which can have a variable wave form is transmitted by output 8.31 which generates a voltage at the terminals of the buzzer 26a which thus will produce a first sound. A different sound may be produced by the transducer 26 when a signal is sent by the output 8.30 to the base of transistor 26b which then begins to conduct. A different voltage is then generated at the terminals of the buzzer 26a and a second sound is produced. Such different sounds can be used in order to announce performance of various functions by pager 1.

FIG. 4 shows a simplified schematic of the intelligent memory 5 which basically comprises the unit 6 for data processing, memory area 7, ROM 27, register stack 28, the microprocessor interface 29 and the decoder interface 30. Terminals 5.5 to 5.12, already described, are connected to the microprocessor interface 29 while terminals 5.1 and 5.2, also hereinbefore described, are connected to the decoder interface 30. The input providing the clock signal of 32 kHz to the intelligent memory 5 is connected to the data processing unit 6. Furthermore, the microprocessor interface 29 comprises a test input 5.13, a capacitor 5d which may have a value of 15 nF being connected between the negative supply line 16.2 and an input 5.14 of memory area 7.

Intelligent memory 5 also comprises address and data buses 5e to 5k connected between the various internal elements of memory 5 in order to assure communication and data transfer among themselves. ROM 27 contains the programs necessary in order to bring about operation of memory 5. In the embodiment described herein, memory area 7 is a RAM having a capacity of 512 octets and intended to memorize the message signals coming from decoder 4 and the internal variables of the system, the stack of registers 28 forming on the one hand a memory for temporary storage of data used for manipulating message information in the memory area 7 and on the other hand the stack pointer and program counter.

It will be understood by those skilled in the art that calls are normally transmitted more than once from a central station to a given pager in order to guarantee good reception by such pager. Consequently, before writing message information from decoder 4 into the memory area 7, intelligent memory 5 may advantageously compare such received message information with two preceding messages which the pager has just received. If the new message information corresponds to one or the other of the two most recent messages, the new message is not written into memory area 7.

As already indicated and as shown on FIG. 5, it is envisaged, in the embodiment of the invention under consideration, to give the memory area 7 a capacity of 512 octets. Such a capacity is sufficient for conferring to pager 1 sufficient information manipulation possibilities so as to render it user friendly.

A capacity of 512 octets requires nine bits in order to permit addressing of octets 0 to 517 in memory area 7. This signifies that for each write-in or read-out operation in this memory area, two transfers each of eight bits are necessary since buses 5e to 5k have a transfer capacity limited to 8 bits at a time. The program stored in ROM 27 is adapted to work with such a double eight bit transfer of which in the present embodiment only nine bits are used. In fact, one may thus, without substantially changing the program contained in ROM 27, easily increase the capacity of memory area 7 up to a maximum of 65 kilo-octets, which is a value largely exceeding the capacity of 4 kilo-octets, which would already constitute a value giving a large degree of user comfort. Such an extension of the memory capacity would give the pager the possibility of carrying out more control functions by the user and also a greater capacity of storing received message information.

Memory area 7 comprises address segments 7a, 7b and 7c (FIG. 5), segments 7a and 7b of which comprise addresses 0 to 489 and are available for the storage of message information received from decoder 4 and segment 7c comprises addresses 490 to 511 and contains internal variables of intelligent memory 5.

Address segment 7a comprises addresses 0 to 300 and is used by the data processing unit 6 as a circular buffer in order to store message information coming from decoder 4 so that the memory location assigned to the circular buffer is initially sequentially filled with received message information. Following storage of the message information in each available address of the circular buffer, the oldest message information is transferred at the moment when the most recent message information is received by intelligent memory 5. By default address segment 7b occupying addresses 301 to 489 is used as a protection section in which is stored message information coming from the circular buffer which the user does not wish to have transferred.

Address segment c comprises the following addresses which are used by the data processing unit 6 in order to manipulate data found in the memory area 7:

In addition the following codes which may be stored in the memory area 7 are interpreted by the data processing unit 6 to have special meanings:

Reference will now be had to the operation of the data processing unit 6, and the functions that are successively performed by the intelligent memory 5 when various instruction signals are received from the microcomputer 8. As described previously, the microcomputer 8 is able to indicate to the intelligent memory 5 that it wishes to send an instruction signal, by placing a high level logic signal at the output 8.9. When the output 5.10 is at a high logic level, an instruction signal placed at the outputs 8.1 to 8.4 is read by the intelligent memory 5 when a low-to-high logic transition occurs at the output 8.11. Under these conditions, the following functions may be performed by the intelligent memory 5, where each function code represents the logic state of the outputs 8.4 to 8.1 respectively:

The following functions serve to read from and write to the memory area 7. The actual address of the memory area 7 at which the message information is to be stored or read from must firstly be put into the PTA register. With a high logic level at the output 8.9 of the microcomputer 8, the data present at the inputs 5.5 to 5.8 are treated as instruction signals. The message information can subsequently be transferred to or from the intelligent memory 5 when the logic level at the output 8.9 again goes low.

When an entire octet (2 packets each of 4 bits) has been completely transferred, the position of the pointer PTA stays unchanged. It is therefore possible to copy an already read octet in the RAM 7 without the need to change the position of the PTA. It is only upon the transfer of the first packet of 4 bits, which are the four most significant data bits with the leading edge of the low-to-high logic level transition of the output 8.11 that the PTA will be incremented or decremented and the address changed of the RAM 7 to which it points.

The following functions concern a single complete message, rather than separate octets of message information comprising the message. In order to separate the messages from one another, the code 04 H or 84 H is written with the data packet at the end of each message, and at the start of the following message (header). The PTA must contain the address of the header of the message to be manipulated by the data processing unit 6, so that the following instructions can be executed. If the PTA does not contain this address, an interrupt signal will be provided by a logic high level at the output 5.12 with an error included in the status word.

As can be seen from the foregoing, the intelligent memory 5 according to the invention is thus adapted to receive message information from the decoder 4 in real time, so as to compare the received message with the previously received messages and store chosen message information in a memory area. The intelligent memory 5 is also adapted to copy, delete, move and otherwise manipulate the stored message information and to communicate and exchange data with the microcomputer 8 in a manner which frees the microcomputer 8 from some of the constraints connected with message information reception, storage and manipulation.