Word Processing System

A. Field of the Invention

This invention relates generally to a word processing system and more particularly to a word processing system having a horizontal and vertical scrolling.

B. Background Art

Conventional word processing systems have in the past used a memory in combination with a character generator to generate the raster lines which are provided on a display monitor for displaying characters and character modifiers known as attributes. Such attributes are, for example, an underline, a double underline, or a strike-through. Systems have also been provided which allow the use of horizontal and scrolling techniques. Horizontal scrolling permits the movement of characters horizontally on the display monitor, thus allowing the viewing of a document having a wide format. Similarly, vertical scrolling permits the movement of character lines vertically on the display monitor, thus allowing the viewing of a document having a long format. The technique of windowing has also been known. In windowing the display is divided horizontally, for example, into two windows for the viewing of portions of secondary documents in addition to the one being worked on.

Conventional word processing systems have, however, left much to be desired. The manner in which these systems provide scrolling, either vertically or horizontally, has many drawbacks in flexibility and control. For example, varying the rate of scrolling has been difficult; scrolling a portion of the lines on the display monitor without affecting the remaining portion has been limited. Further, prior systems have not been able to vertically fold a document on the display, freezing the portion of the document to the left of the fold and then horizontally scrolling the right portion. Creating windows on the display monitor and scrolling the lines in one window without affecting the other windows has had many drawbacks. More importantly, conventional word processing systems have not provided scrolling capability in a simple and flexible manner wherein the characters or raster lines appear to smoothly move across the display monitor screen.

An object of this invention is to provide soft scrolling in a simple and flexible manner in which the characters or raster lines appear to smoothly move across the screen.

Another object of this invention is to provide a soft scrolling capability wherein the scrolling rate may easily be controlled.

A word processing system having storage for a plurality of words with each word having character line data and a scroll value. A character generator converts the character line data into a sequence of raster line data. Control means addresses the character generator and converts the character line data into the sequence of raster line data. The control means is responsive to the scroll value for varying the sequence. A display monitor converts the raster line data into physical raster lines for display.

FIGS. 1A and 1B are schematic block diagrams of a word processing system embodying the present invention;

FIG. 2A is a diagrammatic representation of a line image word utilized by the word processing system of FIGS. 1A-B;

FIG. 2B is a diagrammatic representation of an attribute byte formed within the line image word;

FIG. 3 is a diagrammatic representation of a 9.times.12 dot matrix of a display monitor utilized by the word processing system of FIGS. 1A-B to construct characters and attributes;

FIG. 4 is a schematic block diagram of the character generator and driver of FIG. 1B;

FIG. 5 is a timing diagram showing relationships among several signals within the word processing system of FIGS. 1A-B;

FIGS. 6A and 6B are schematic block diagrams of the attribute logic of FIG. 1B;

FIG. 7 is a diagrammatic representation of the "ping-pong" effect when transferring data from main memory to the character generator and driver of FIG. 1B;

FIG. 8 is a schematic block diagram of the scroll logic of FIG. 1B;

FIG. 9 is a diagrammatic representation of a screen buffer within the main memory of FIG. 1B;

FIG. 10 is a diagrammatic representation of the relationship between a page stored in main memory and the screen buffer of FIG. 9;

FIG. 11 is a diagrammatic representation of a single displayed screen showing windowing on the display monitor of FIG. 1B, and

FIG. 12 is a diagrammatic representation of a single displayed screen showing folding on the display monitor of FIG. 1B.

Referring now to FIG. 1 there is shown word processor system 10 embodying the present invention. The heart of word processor system 10 is central processing unit (CPU) 12 which is a conventional microprocessor unit. CPU 12 communicates with its associated I/O devices by way of AD bus 94 and in this manner controls all operations. Operations such as reading and writing are performed by CPU 12, by way of example, to main memory 62, floppy disc controller 28, CRT controller 78, keyboard typewriter serial interface 24, RS-232 interface 26 and RS-422 serial interface 32. Main memory 62 is random access memory (RAM) used by system 10 for storing data to be displayed on CRT monitor 96 and storing the various programs required to operate system 10. Floppy disc controller 28 is utilized for transferring various programs or data between a conventional floppy disc and system 10. CRT controller 78 is used to control the display characteristics of CRT monitor 96. Finally, typewriter interface 24, RS-232 interface 26 and RS-422 interface 32 are utilized to communicate with a conventional keyboard or typewriter, a modem or RS-232 device, and a RS-422 device, respectively.

More specifically, CPU 12 utilizes AD bus 94 as a combined address and data bus. CPU 12 generates a 17 bit address onto AD bus 94 which is used to address main memory 62, read only memory (ROM) 64, and I/O devices 24, 26, 28, 32 and 78. The address information is latched by address buffers 14, which may be conventional address latches consisting of three hex D-type flip-flops, and gated onto AB bus 90 by way of bus drivers 16, which may be three conventional hex tri-state buffers. After the address has been latched by address buffers 14, AD bus 94 becomes a data bus. In case of a write operation, CPU 12 generates a 16 bit data word onto AD bus 94; the data is then gated onto BD bus 88 by way of bus drivers 18, which may be conventional tri-state quad bus drivers/receivers. In case of a read operation where data is read by CPU 12, data from BD bus 88 are gated onto AD bus 94 by activation of bus drivers 18 in the other direction. Thus, AD bus 94 serves as an address bus and as a bidirectional data bus.

The latched address bits from address buffers 14 are also placed onto A bus 92 and transmitted to I/O port address decoder 22, the latter selecting which I/O device is to be written to or read from. The selected I/O device, such as floppy controller 28 or RS-232 interface 26, accepts the address information placed on A bus 92, and either reads or writes data onto BD bus 88 from the properly selected address location.

In operation, bus timing on BD bus 88 is divided into two cycles, direct memory access (DMA) cycle and CPU cycle. DMA cycle, as will be explained later, is the time during which non-CPU operations may occur. Such operation may be, for example, floppy disc controller 28 directly accessing main memory 62, or displaying screen data on CRT monitor 96 directly from main memory 62 without CPU 12 intervention. The other cycle, CPU cycle, is the time during which the CPU may access main memory 62 or perform operations with the various I/O devices. During CPU memory access, the operation is as follows: For a write operation, CPU 12 first places the address on AD bus 94 which is then latched into address buffers 14. During the CPU cycle, the address is gated onto AB bus 90 by way of bus drivers 16. After the address has been latched, AD bus 94 becomes a data bus, and CPU 12 places on the bus the data to be written into the specified address location in memory. During the same CPU cycle, the data is placed onto BD bus 88 by enabling bus drivers 18. Memory 62, in a manner that will be explained later, then places the data on BD bus 88 at a specified memory location dictated by the address on AB bus 90. For a read operation, after the address has been latched into address buffers 14, AD bus 94 goes into a high impedance state to permit it to receive data from main memory 62. At the appropriate time, during the CPU cycle, memory 62 places the data requested by CPU 12 onto BD bus 88, and bus drivers 18 are enabled in the appropriate direction to send the data to CPU 12 by way of AD bus 94.

All I/O read or write operations between CPU 12 and an I/O device, such as floppy controller 28 or interface 24, 26, 30 or 32, are performed in substantially the same manner as read or write operations between CPU 12 and main memory 62. The data is placed on BD bus 88 and sent to an I/O device or CPU 12, depending on whether a write or read operation is to be performed, respectively. Address information is placed, however, on A bus 92 and originates from CPU 12 by way of address buffers 14. In all cases, I/O port address decoder 22 selects the I/O device which will be read from or written to by CPU 12. As in the case of CPU to memory operations, data can only be placed on BD bus 88 during a CPU cycle time. It will be understood that all I/O read or write operations contain wait states to ensure that an I/O device will respond to a write I/O or has adequate time to receive data in the case of a read I/O.

Also shown in FIG. 1 is interrupt controller 20. Communications between an I/O device and CPU 12 are initiated by an interrupt controlled by controller 20. A device can cause an interrupt by providing a high level signal on one of the lines 20a through 20h. The interrupt controller then responds by issuing an interrupt request to CPU 12.

Screen interrupt, SINT 20a is issued by controller 78 to notify CPU 12 that a new screen can be displayed on CRT monitor 96. RXRDY 20b is issued by serial interface 24 to notify CPU 12 that it has a character ready for input to the CPU. TXRDY 20c, transmitter ready, signals CPU 12 that a character may be transmitted. In a similar manner, CRXRDY 20g and CTXRDY 20h (receiver ready and transmitter ready, respectively) are issued by interface 26. RINT 20f is issued when interface 26 senses a ring from a modem. Finally, FINT 20d, floppy interrupt, is issued by floppy controller 28 upon completion of a command for read or write.

As already mentioned, system 10 has two types of cycles, a DMA cycle and a CPU cycle. Fifty percent of the throughput on BD bus 88 is allocated to the DMA cycle and the other fifty percent to the CPU cycle. As such, half of the time is dedicated to performing direct memory access operations and half of the time is available to the CPU to perform instruction fetches and data transfers. During DMA cycles, memory operations are always performed. Lines of screen information to be displayed on CRT monitor 96 are contained in main memory 62. This information is continuously read to supply the data to be displayed on the CRT monitor. Hence, DMA operations for displaying data on CRT monitor 96 imposes a substantial demand on BD bus 88. On the other hand, when a DMA transfer occurs between memory 62 and floppy controller 28 only a small demand is imposed on BD bus 88. As an example, when a floppy data transfer is initiated only 2 DMA cycles are necessary every 32 microseconds, whereas a CRT monitor data transfer requires as many as approximately 37 DMA cycles every 32 microseconds (a DMA cycle is 432 nanoseconds).

Main memory 62 is a conventional memory comprised of 128 KB of RAM and a memory address decoder. The RAM consists of 64 dynamic 16 K by 1 bit random access memory chips. The random access memory requires refreshing every 2 milliseconds to reliably retain data. As will be explained later, the design of system 10 is such that this refresh cycle is performed during the course of normal operation of reading main memory 62 to provide line buffers 70 and 72, shown in FIG. 1, with the information to be displayed on CRT monitor 96. The memory address decoder of main memory 62 is a conventional decoder for accepting the address information on AB bus 90 and determining the row and column of memory in which data is to be written to or read from. Lastly, coupled to main memory 62 is memory data buffer 66 and is comprised of four bi-directional tristate transceivers which may be conventional transceivers. This data buffer moves the data presented on BD bus 88 into main memory during a memory write operation, and moves data from main memory onto BD bus 88 during a memory read operation.

Also shown in FIG. 1 is boot ROM 64, which is a read only memory used during the power up sequence of system 10. A boot loader program contained in ROM 64 initializes the circuitry required for main memory 62 refresh and for CRT monitor 96 display information. ROM 64 is also utilized to unload the first program from a floppy disc by way of floppy controller 28. The ROM consists of two ROM chips each containing 2 KB of data eight bits wide. ROM 64 is addressed by CPU 12 by way of AB bus 90 and the data, consisting of 16 bit parallel data, is placed onto BD bus 88 by way of data buffer 66. See Appendix A.

Having described main memory 62, the video section will now be described. Still referring to FIG. 1, the major elements of the video section are line buffers 70, 72, bus transceivers 74, 76, CRT controller 78, attribute logic 80, scroll logic 82, character generator and driver 84, and CRT monitor 96. In general, data is fed from memory 62 to character generator and driver 84, the latter including a conventional character generator ROM which converts the data into a 9.times.12 dot matrix format. Character generator and driver 84 also includes a shift register which converts the parallel dot matrix format into a serial data stream for output to CRT monitor 96, as will be explained later. This serial data stream may be modified by attribute logic 80 or CRT controller 78 before being sent to CRT monitor 96. Modifications by attributes, as will also be explained later, include underlining a character, striking through a character, double underlining a character, etc. Modifications by CRT controller 78 include the positioning of a cursor on the monitor. The CRT controller also generates horizontal and vertical sync to the monitor, and generates raster line numbers to the character generator by way of scroll logic 82. These numbers may be modified by scroll logic 82 when it is desired to scroll the lines of data presented on CRT monitor 96. When scrolling occurs, these lines visually appear to move up or down on the monitor. On the other hand, when scrolling is not desired, scroll logic 82 does not modify the raster line number presented by CRT controller 78, thus allowing the display on the monitor to appear stationary.

Data representing lines of characters to be displayed on CRT monitor 96 are fetched from main memory 62 by way of transceivers 74, 76 and stored in line buffers 70, 72. Such data is shown in FIG. 2A and represents a single line image format. Line format 100 is comprised of 256 bytes, each byte having 8 bits of data. It will be understood that, in general, the software for system 10 scatters character line images in random places in main memory 62. Thus, the first line 100 is placed at one location in memory, the second line 100 is placed at a second location, which is not contiguous to the first, and so on. Accordingly, the first two bytes of line format 100 contain the beginning main memory address of the next character line image, as shown by bytes 108. The next byte, scroll prefix 106, produces a space at the beginning character position of every line displayed on CRT monitor 96 as will be explained later. The next byte following the scroll prefix is scroll value 104. The scroll value, as will be explained later, can be any value between 0 and 11. When the scroll value is 0, no scrolling motion occurs on CRT monitor 96; when different from 0, scrolling motion does occur. Beginning at byte position 4, any mix of character bytes and attribute bytes can exist in line format 100. Each character byte is comprised of 8 bits of data and is used by character generator and driver 84 to output the corresponding character to CRT monitor 96. Such character byte may represent a letter, a number, a punctuation mark, or any other character that may be typed on a document. Similarly, an attribute byte is comprised of 8 bits of data, as shown in FIG. 2A. A `1` in bit location 7 of attribute byte 110 indicates that this byte is indeed an attribute. Such attribute may be an overline, underline, strike thru, double underline, right line, left line, bold and inverse.

The manner in which an attribute is displayed on a 9.times.12 dot matrix on CRT monitor 96 is shown in FIG. 3. There shown is a single character, by way of example, `X` 124. Any character may occupy dot positions 1 thru 7, having columns 0 and 8 always blank. Hence attributes, left line 132 and right line 134 are placed into columns 0 and 8, respectively. Four additional attributes are shown, overline 122, strike through 126, underline 130 and double underline 128. It will be understood that strike thru, underline and double underline are mutually exclusive attributes. These attributes are thus simple overlays upon a character to which they apply. There are two attributes which are handled differently--inverse and bold. The first is a situation where the dot pattern is logically inverted to the monitor; in other words, the monitor screen background is painted white and the character lines are painted black (the dots representing the characters remain unlit). The second attribute, bold, is a situation where the dots representing a character are stretched wider, making it appear bolder or more pronounced than a normal unbolded character.

As mentioned earlier, any mix of character bytes and attribute bytes can exist in line format 100. One exception, however, is that every attribute byte must be separated from any subsequent attribute byte by at least a single character byte. It will further be understood that CRT monitor 96, which is a conventional display monitor, permits displaying all character bytes until its screen is filled with 80 characters across a line. Very briefly, the monitor screen is comprised of 324 raster lines containing 738 dots per line. Since each character is built within a 9.times.12 dot matrix, there are 27 character lines defined, each one containing 12 adjacent raster lines. Of these 27 character lines, 2 are blanked during vertical retrace, leaving 25 visible character lines on the screen. As far as the horizontal trace, since the first 9 dots are always displayed as a space and the last 9 dots are blanked during horizontal retrace, only 80 characters are visible on the screen per line. These parameters are programmed into CRT controller 78 by way of internal register files, thus maintaining proper display operations. The controller register files are shown in Table 3.

Referring now to FIG. 4, there is shown character generator and driver 84 in more detail. Bytes of character data placed on M-bus 92 enter latch 142, which may be comprised of 2 conventional latches. Latch 142 is loaded by OR gate 144 during the absence of INHIBIT 146, and during the presence of MCLK 156, a clock signal provided by timing generator 154. It will be understood that INHIBIT 146 disables latch 142 during the presence of a scroll value or an attribute byte. With latch 142 enabled, 7 bits (M0-M6) are passed from M-bus 92 into character generator ROM 140 by way of bus 150. As mentioned earlier, ROM 104 converts the 7 bits (8th bit is always 0) into a 9.times.12 dot matrix format. Hence, for every character byte appearing at the ROM input, a corresponding single (9.times.1) dot row is output onto lines 148. In order to complete the 9.times.12 dot matrix, there exists 12 entries in ROM 140 corresponding to the 12 raster lines making up a full character line on CRT monitor 96. These 12 entries are counted by scroll logic 82 and sent to ROM 140 by way of lines 152. These lines consist of 4 bits (L0- L3) which relate to the raster number address of 1 to 12. In this manner, ROM 140 outputs 12 rows of dot patterns to make up a full character line on the display. It will be understood that ROM 140 outputs onto lines 148 one complete raster line pattern corresponding to the 256 bytes of data placed on M bus 92, then ROM 140 outputs the next raster line, and so on until the 12 raster lines are completed to make up a full character line. Upon completion of this line, ROM 140 is ready to read the next 256 bytes of data placed on M bus 92, and so on until the display is completed with a maximum of 25 character lines.

The parallel dot pattern from ROM 140 is loaded into shift registers 172 and 174. As shown, seven parallel bits per character are loaded into registers 172 and 174 by SRL 158, the latter enabling the shift registers by way of inverter 170. The parallel bits are shifted out serially into OR gate 180 by VCLK 160, a clocking signal from timing generator 154. The timing relationships of these signals are shown in FIG. 5.

As shown in FIG. 5, VCLK 160 is divided by nine to produce MCLK 156 and SRL 158. It will be understood that VCLK 160 may be an 18.432 MHz signal from a crystal oscillator. This signal represents the basic CRT monitor dot frequency and, therefore, all timing for the video, the CPU and the memory is derived from it. VCLK 160 is divided by nine in a conventional manner by timing generator 154 to generate MCLK 156 and SRL 158. The nominal period of these signals is 488 nanoseconds corresponding to one character period on the CRT monitor screen.

Since ROM 140 only places a 7-bit dot pattern into the shift registers and since a total of 9 dots are available per character, as shown in FIG. 3, there exists two additional inputs that may be placed in shift registers 172 and 174. Such inputs are provided by LEFT 164 and RIGHT 162 by way of attribute logic 80. As shown in FIG. 4, LEFT 164 is so placed that it is shifted out first from shift register 174 to OR gate 180; RIGHT 162 is shifted out last, i.e. in the ninth position per character dot matrix. In this manner, if LEFT 164 is activated for the entire 12 raster lines, a left attribute is positioned in the first column of the 9.times.12 matrix, as shown by left line 132 in FIG. 3. Similarly, if RIGHT 162 is activated for the entire 12 raster lines, a right attribute is positioned in the last column of the matrix, as shown by right line 134.

Leaving the shift registers, the serialized dot pattern containing a raster line of characters, and perhaps a left or a right attribute enters OR gate 180. At this point any horizontal line attribute, such as overline 122, strike through 126, double underline 128 or underline 130, shown in FIG. 3, may be OR'ed by gate 180. The dot pattern for making up the horizontal line attribute, which enters by way of HLAI 176, will be described in detail later. When CDENA 200, a CRT device enable signal from CRT controller 78, is activated, AND gate 182 passes the dot pattern to EXCLUSIVE-OR gate 186. At this point INVERSE 202 and CURSOR 204 are added to the data stream through EXCLUSIVE-OR gate 184. It will be understood that INVERSE 202, originating from attribute logic 80, provides the inverse attribute characteristics on the display; CURSOR 204, originating from CRT controller 78, provides a cursor on the display.

The serialized dot stream, at this point containing all the information to complete a single raster line on the display, enters flip-flop 196. The latter outputs the dot stream, when clocked by VCLK 194 at the basic dot frequency described earlier. The dot pattern is then outputted as video to CRT monitor 96 by way of AND gate 198. When it is desired to make a character brighter, the dot stream pattern is made wider by BOLD 188, an attribute supplied from attribute logic 80. BOLD 188 simply stretches the ON time of each video pulse by way of OR gate 190.

Having described the generation of video pulses to the display, the manner in which the attributes are logically generated will now be described. Referring to FIGS. 6A and 6B, there is shown attribute logic 80. When an attribute byte (M0-M7) is placed on M-bus 92, bit M7 becomes high, as shown in FIG. 5. This in turn causes ATCLK 280 and ATCLK 282 to become high and low, respectively. Assuming that CDENA 200 from CRT controller 78 is enabled, bits M0-M6 are latched into first rank registers 220 and 228. The same 7 bits are then loaded into second rank registers 222 and 230, upon activation of SRL 158. If the attribute byte, shown in FIG. 2B, has bit positions 2 and 3 active, as an example, then M2 and M3 on M-bus 92 are both high. Accordingly, RIGHT 162 having been inverted by inverter gate 224, and LEFT 164 become high and low, respectively. Both are then presented to shift registers 172 and 174 for providing the appropriate dot pattern to place right line and left line attributes on CRT monitor 96, as described earlier. The remaining attributes when present, are latched into register 226, at the start of the next SRL 158 cycle and upon the output of AND gate 236 becoming low. It will be noted from FIG. 6A that OVERLINE 250 is high, when the M4 bit of an attribute byte is high. Also LOWERLINE 252 is high, when AND gate 232 decodes both M5 and M6 to be high; STRIKETHRU 254 is high, when AND gate 234 decodes M5 to be high and M6 to be low. Moreover, UNDERLINE 256 is high, when M6 is high. It will further be noted that when LOWERLINE 252 is high, UNDERLINE 256 is also high, thus producing a double underline attribute. Finally, BOLD 188 and INVERSE 202 are generated, when the M0 and M1 bits of an attribute byte are high, in the manner shown in FIG. 6A.

For an understanding of how the following attributes--overline, strikethru, lowerline and underline--are enabled at the appropriate raster line, reference can be made to FIG. 6B in conjunction with TABLE 1. As shown, HLAI 176 is produced by combining output 354 and output 356 by way of OR gate 260. These in turn are controlled by inputs into multiplexor 258 which are OVERLINE 250, STRIKETHRU 254, LOWERLINE 252, UNDERLINE 256, strobe line 350 and strobe line 352. Since the overline attribute is placed at the first row of the 9.times.12 matrix, multiplexor 258 produces a high on output 354 whenever lines L0-L3 from scroll logic 82 indicate a count of zero. Since the strikethru attribute is placed at the seventh raster line, multiplexor 258 produces a high whenever lines L0-L3 indicate a count of six. Similarly, output 356 is high whenever LOWERLINE 252 and UNDERLINE 256 are high, and lines L0-L3 indicate a count of nine and eleven, respectively.

As already mentioned, system 10 constructs complete CRT monitor screen images in main memory 62. These screen images are each divided into 25 visible character lines, where each character line is comprised of 256 bytes. Since the first two bytes in a character line always contain the main memory starting address of the next character line, system 10, after getting started at the first line, is able to fetch an entire screen image without any software stimulus. When the next screen image is started, the software must direct the system to a new starting address for the first line and the process repeats indefinitely. The manner in which system 10 can fetch an entire screen image from memory will now be described.

Fetching character lines from main memory 62 is performed by way of DMA operations. The starting address of the first character line on the screen is loaded into CRT address register 42 by way of BD bus 88. This starting address is loaded under software control initiated by an interrupt signal, SINT 20a, from CRT controller 78 to interrupt controller 20, as shown in FIG. 1. Having the starting address, address register 42 transmits the same to adder 58, which in turn transmits the same to main memory 62 by way of bus drivers 60. Bus drivers 60, it will be understood, are enabled during the DMA cycle to ensure nonintervention with CPU 12 operations. Having received the starting location, main memory 62 outputs from that location onto BD bus 88 the first character line data. The first two bytes of this character line are then loaded into CRT address register 42 and the process repeats.

It will be noted that CRT write counter 48 increments once for each byte in a character line fetched from memory. Hence, CRT write counter 48 counts from zero to 255, corresponding to the 256 bytes per character line. The value in counter 48 is summed with the value in register 42 by adder 58 to produce the main memory address of each data byte in the character line image. This process is repeated for every character line of data fetched from main memory 62 until the screen is completed.

The lines of data placed by main memory 62 onto BD bus 88 are sent to M bus 92 by way of line buffers 70 and 72, as shown in FIG. 1. The line buffers are split into two halfs such that while one half is being loaded from main memory, the other half is sending a line image onto M bus 92. Thus, line buffers 70 and 72 "ping-pong" between a read from memory operation and a write to character generator 84 operation. It will be understood that each line buffer is comprised of a conventional memory chip having two 1K.times.4 arrays. Line buffers 70 and 72 toggle between a read and write operation under control of scroll logic 82, as will be explained later. In addition, transceivers 74 and 76 toggle between receiving data from BD bus 88 for a line buffer read operation and transmitting data onto M bus 92 for a line buffer write operation. Furthermore, conventional multiplexors 54 and 56 each toggle between sending an address from counter 48 to a line buffer during a write from main memory operation and sending an address from counter 50 to a line buffer during a character generator read operation. It will be noted that CRT write counter 48 addresses main memory and one line buffer simultaneously, thus counting from 0-255 and allowing line buffer storage of a complete character line image of 256 bytes. On the other hand, CRT read counter 50 addresses only a line buffer at the beginning count of 2, thus allowing M bus 92 to see all bytes of line data except for the next address line bytes shown in FIG. 2A.

As mentioned earlier, system 10 has a soft scrolling capability where a line on the CRT monitor screen can be made to visually appear as moving up or down. Such movement is provided one raster line at a time and as a result, a character line having previously occupied 12 physical rasters in one position begins to spill into another adjacent 12 physical rasters. Hence, during scrolling, any 12 physical rasters may contain data from two character line images. Since character generator 84 can only read data from one line buffer at a time, it follows that each line buffer must contain two complete character line images. Therefore, the timing of system 10 is such that two complete character lines are loaded into a line buffer, while the other buffer is dumping one character line or two character lines to character generator 84. Whether one character line or two character lines are dumped by the buffer depends on which of the 12 physical raster lines are being painted on the monitor display. This operation is functionally illustrated in FIG. 7.

In operation during none scrolling conditions, line buffer 70 receives from main memory 62 two character lines, 1 and 2, as shown functionally by 70a. The line buffers are then toggled so that line buffer 72 can receive lines 2 and 3, as shown by 72a. While line buffer 72 is receiving the data, buffer 70 dumps line 1 onto M bus 92, as shown by 92a. After again toggling, line buffer 70 receives lines 3 and 4, as shown by 70b; end buffer 72 dumps line 2, as shown by 92b. After another toggle, buffer 72 receives lines 4 and 5, as shown by 72c; and buffer 70 dumps line 3, as shown by 70c. This action continues until the entire 25 lines have been read from main memory and dumped onto M-bus 92 for eventual display. Thus, it will be noted that two complete lines are read into each buffer; and that during none scrolling operations, the character line images are sent to the display from the shaded top quadrant of the line buffer shown in FIG. 7.

It will be recalled that the line buffer being read to the display is always read 12 times, corresponding to the 12 CRT rasters per character line. By way of example, completing 12 CRT rasters on the display may occupy 620 milliseconds. This allows the system 620 microseconds to fill the other buffer line with 2 character line images. Accordingly, DMA rate must be fast enough to access 512 bytes of data within less than 620 microseconds in order to complete two character lines.

If vertical scrolling is engaged, the previously described operation remains the same, except for the manner in which character lines are dumped onto M-bus 92. Thus, two complete character lines are still read into each buffer, as shown in FIG. 7, and each line buffer being read to the display is still read 12 times corresponding to the 12 CRT rasters per line. However, during scrolling, images are sent onto M-bus 92 from either the top or bottom quadrant shown in FIG. 7 according to the actual raster being painted on the display. By way of example, assume that scrolling has already moved up lines on the display so that the top 5 rasters of a character line have spilled into the bottom 5 rasters of an adjacent character line. Therefore, the next display screen to be painted must be such that one additional raster line will spill into the adjacent character line; in other words, the top 6 rasters of a character line must spill into the bottom 6 rasters of an adjacent character line. As a result, line buffers 70 and 72 send images onto M-bus 92 in the following manner: Line buffer 70 sends character line 1 onto M-bus 92 for the duration required to paint its 6 bottom rasters, and then sends character line 2 onto M-bus 92 for the duration required to paint the latter's 6 top rasters. After toggling of the line buffers, line buffer 72 then sends character line 2 onto M-bus 92 for the duration required to paint its 6 bottom rasters, and then send character line 3 for the duration required to paint the latter's 6 top rasters. The toggling continues in this manner until all 25 character lines have been painted on the display each buffer continuously sending for half the time one character line image and for the second half its other character line image. Thus, during scrolling, images are sent onto M-bus 92 from either the top or bottom quadrant shown in FIG. 7.

It will be understood that the software of system 10 controls whether the display moves up or down. If scroll value 104, shown in FIG. 2a, is set to zero, then no scrolling occurs. If, however, set to any other value (up to 11), scrolling occurs. Furthermore, if the software increments the scroll value once per screen, the screen images visually appear to move up; if, however, the software decrements the scroll value once per screen, the screen images appear to move down. It will be noted that such movements are visually smooth and soft to the eye since for each increment or decrement per screen, the images only move up a single raster line. By way of example, if the screen is painted 60 times per second and there are 12 rasters per line, the scroll rate is 5 lines/second (60/12=5).

As previously mentioned, the actual raster line painted on CRT monitor 96 is controlled by scrool logic 82, shown in detail in FIG. 8. Scroll value 104 of character line 100 is placed on M-bus 92. The first four bits 420 (M0-M3) enter scroll value latch 402, which is a conventional latch. The latch is enabled by EOL 416 from controller 78, marking the end of the 12th raster line. Bits 420 and physical raster bits 414 (RA0-RA3) are combined by adders 404 and 406, the latter being conventional adders. It will be noted that RA0-RA3 represent the physical raster line position being painted on the display monitor, and can be any value from 0 to 11, as shown in Table 2. After being added, bits 152 (L0-L3) are outputted to character generator 140 for controlling which raster line is actually painted on the display. By way of example, Table 2 shows the states of bits 152 for all possible values of physical raster bits 414, when the scroll value is set to 6. It will be noted that if scroll value 104 is equal to zero, then physical raster bits 414 are equal to virtual raster bits 152. Finally, MUXS 400 is sent to line buffers 70 and 72 to control which one of the two character lines is to be dumped onto M-bus 92, as described earlier. In the example shown in Table 2, note that when bits 152 are equal to 11, MUXS 400 switches state to begin dumping the next character line to the character generator.

Having described the painting operation of character lines on CRT monitor 96, the manner in which these character lines are built in main memory 62 will now be described. Organization of such lines in the memory can best be understood in connection with FIG. 9. There shown is a diagrammatic representation of main memory 62 in which screen buffer 500 is formed. Screen buffer 500 is comprised of 26 line images each having 256 bytes as previously described and shown in FIG. 2A. The organization of line images 100 provides the capability to chain link each line to the next by the first two character positions pointing to the address of the next line image. Hence, line 1 points to line 2, line 2 points to line 3 and so on, until line 25 is addressed. However, line 26 is an unmapped line and is not displayed. It will be understood that physically each character line is located at random location in main memory 62, but is easily found as a result of each character line pointing to the next line.

As previously described, software control provides the starting address of the first image line. The screen interrupt, SINT 20a, informs CPU 12 to load the starting address of the first image line belonging to the next screen display. The CPU then points to the first image line. All subsequent lines are loaded without CPU 12 intervention by way of system 10 DMA operation. It will also be recalled that only 25 image lines are displayed on CRT monitor 96. Thus, line 26 in screen buffer 500 is not displayed, but is utilized for purposes to be explained later.

For every complete display on monitor 96 there exists one specific configuration of 26 line images stored in screen buffer 500. Once a complete screen is painted on the monitor, screen buffer 500 is changed by the software of system 10 to reflect what is to be painted on the next screen. Thus, screen buffer 500 may be thought of as being a software snapshot of a complete screen display; for every new screen, a new snapshot exists. This can best be understood in connection with FIG. 10. There shown is page 502 which may be a software representation of a page in main memory 62, originally typed by the user and brought into memory 62 by way of floppy controller 28. It will be noted that page 502 has more than 25 image lines of characters and hence cannot all be displayed on CRT monitor 96. Also shown is screen buffer 500 containing 25 image lines 502d through 502g and an unmapped 26th line. Although shown in consecutive physical location, it will be understood that lines 502d through 502g are randomly located in memory 62 and are displayed on CRT monitor 96, as previously described.

By way of example, assume that the scrolling function of system 10 is off. For every screen painted on the monitor, screen buffer 500 is configured to contain the same image lines, lines 502d through 502g and a 26th line. The 26th line is not displayed. Assume next that it is desired to display lines 502h and 502i of page 502 on the display. In other words, it is desired to scroll up page 502 by two lines, and make lines 502d and 502e eventually disappear off the top of the display. Accordingly, screen buffer 500 is twice reconfigured by the software of system 10. First, lines 502e through 502h are moved up into lines 1 through 25, respectively; and line 502d is moved into line 26 of the buffer. Subsequently, lines 502e through 502h are placed onto BD bus 88 and system 10 soft scrolls the lines on the CRT monitor one raster line at a time in a manner described previously. Following the first remapping, screen buffer 500 is again remapped by the software so that lines 502f through 502i are moved up into lines 1 through 25, respectively; and line 502e is moved into line 26 of the buffer. Subsequently, lines 502f through 502i are placed onto BD bus 88 and system 10 continues scrolling the lines on CRT monitor 96.

It will be understood that new lines need not actually be brought into screen buffer 500. The screen buffer may be remapped simply by reorganizing a link list table identifying all the pointers linking the lines in their order of placement onto BD bus 88. This table may be reorganized by the softward of system 10 upon receipt of the screen interrupt, SINT 20a, from CRT controller 78.

The building of line buffer 500 and the management of the storage location in which it appears is provided by the software of system 10, and is incorporated herein as Appendix A, appended at the back of this disclosure. As textual characters are entered by way of keyboard typewriter interface 24 or floppy controller 28, the line images are built under control of the software by the coordination and control of CPU 12 fetching the appropriate software programs shown in Appendix A.

By way of another example, assume that the user desires to add a new line onto page 502 between lines 502d and 502e. Assume further that CRT monitor 986 is displaying the contents of screen buffer 500, visually showing lines 502d through 502g. Under software control, CPU 12 remaps the contents of screen buffer 500 by placing the new line into position 26. If the user desires to scroll up the new line to the desired position, the software again reorganizes the line buffer by remapping the list table and having line 502d point to the new line and having the new line point to 502e. At the next screen interrupt, the software increments the scroll value for 502d and new image lines in the screen buffer. The newly organized image lines are then placed onto BD bus 88 and system 10 soft scrolls the images in a manner previously described. Line 502d appears to move off the screen and the new line, originally occupying position 2, is soft scrolled into position 1. The remaining lines 502e through 502g appear to remain stationary in position. On the other hand, if the software decrements the scroll value for the new line and lines 502e through 502g, line 502d appears to remain stationary in position, and the new line and remaining lines 502e through 502g appear to soft scroll downward on the display. In this manner, the new line is placed between lines 502d and 502e, and line 502g is scrolled off the display.

Another capabilty of system 10 is the creation of a windowing facility. The windowing facility divides the display screen horizontally into main and secondary windows for the viewing of portions of secondary windows in addition to the one being worked upon by the user. Both windows are made independently scrollable, in a manner to be described. Hence, the user may copy portions of text from the secondary window into the main window area.

Referring now to FIG. 11, there is shown display 510 of CRT monitor 9i6 having main window 512 and secondary window 514. It will be noted that main window 512 contains lines 516a through 516e belonging to a page having been stored by the user, and secondary window 514 contains lines 520a through 520e belonging to another stored page. Line 518, occupying position 11 of the screen, is an inverse video line providing a convenient method of visually separating both windows. It will be understood that line 518 may be formed by providing inverse attribute bytes in character line image 100 of FIG. 2A, in a manner previously described.

In order to display windows 512 and 514, screen buffer 500 is mapped by the software so that line 516a points to line 516b, line 516b points to line 516c, and so on until line 516e points to the inverse video line 518. Continuing in the same manner, line 518 points to line 520a, line 520a points to line 520b, and so on until line 520d points to line 520e.

If the user desires to enter a new line below line 516e in window 512, the software performs the following operation. The new line is brought into screen buffer 500 by having it occupy the 26th position in the buffer. Thereafter, line 516e is remapped to point to the address of the new line, and the new line is pointed to line 518. At the initiation of a screen interrupt, the scroll value in lines 516a through 516e and the scroll value of the new line are incremented by one. For the next 12 raster lines, system 10 is effective to soft scroll the new line and lines 516a through 516e up the display, in the manner previously described. Thus, line 516a is moved off the display and the new line is softly brought into the display immediately above inverse video line 518. Lines 518 and lines 520a through 520e remain stationary.

In a similar manner, a new line may be brought into window 514 without affecting window 512. By incrementing the scroll value of lines 520a through 520e and the scroll value of the new line at position 26 of screen buffer 500, window 514 may be made to visually appear softly scrolling upward against line 518. Hence, line 518 may be visualized to be a stationary wall against which scrolled lines are moved, and made to disappear one raster line at a time. In addition, a new line may also be inserted between existing lines of a window (for example, placing a new line between lines 516b and 516c of window 512) in a manner previously described, but without affecting the other window. Furthermore, it will be understood that display 510 may contain several windows each separated by a different wall.

Windows may be closed dynamically in a manner similar to their creation. Since windows are considered subsets of each other, i.e. window 514 is considered by the software to be a subset of window 512, the user closes window 514 and permits the display lines originally occupied by window 514 to be available for window 512. Closing a window causes screen buffer 500 to be remapped whereby blank lines, created by bytes causing character spaces, are moved into the buffer, one line per screen interrupt. The blank lines are soft scrolled up CRT display 510 until all character lines in window 514 appear to roll off the display leaving blank character spaces. Window 512 then contains 10 character lines, whereby lines 11 through 25 are blank.

Having described the manner in which system 10 is effective to soft scroll line images vertically up or down the display, another operation will now be described. Such operation, known as folding, is effective to cause character lines to move horizontally, either left or right, on CRT monitor 96. The user is enabled to position the display cursor to a desired position and cause a vertical inverse image to appear on the CRT monitor. The columns positioned to the left of the inverse image line are frozen and the columns positioned to the right are scrolled toward the inverse image line. In this manner the entry of information such as budgets and financial statements requiring a wide format is facilitated. The primary aspect of this feature can best be illustrated by examining FIG. 12.

Referring to FIG. 12, there is shown display 510 having vertical inverse video line 534 separating frozen section 530 and horizontally scrolling section 532. Vertical line 534 is created by having the software build an inverse attribute byte and a blank character byte at position `n` of each character line image. The software then modifies each character line once per screen interrupt in the following manner. Each character byte beyond position `n` is moved to the left by one position. In other words, a character byte initially occupying space `n+3` is moved into space `n+2`; a character byte initially occupying space `n+2` is moved into space `n+1`; a character byte initially occupying space `n+1` is moved against vertical wall 534 and disappears. In a similar manner, all other character bytes in a line are moved to the left by one position and a new character byte is moved into the 80th position. At the next interrupt, the software again moves every character byte one position to the left. In this manner, section 532 of display 510 appears to scroll to the left. It will be noted that the pointers linking each image line in screen buffer 500 need not be modified since the vertical position of each line remains stationary.

Another feature of system 10 is the means of providing editing marks in the form of overlining, underlining, double-underlining, striking-through, right lining and left lining. The manner in which these attributes are provided on CRT monitor 96 has previously been described. It will be recalled that the editing marks are formed within the 9.times.12 dot matrix reserved for each character. Entry of a strike-through, for example, permits the user to display the character simultaneously with the strike-through without having to take up additional matrix space. The software of system 10 has the capability to edit text by striking through portions of text and then placing the new text immediately afterwards. The new text is indicated by the software by addition of an overline attribute. It will be understood that the software establishes an editing mark text file which maintains a table of text to be inserted following the text to be struck-through. Depending upon what is desired for display, the software modifies the grouping of bytes within each character line image. The modified groupings are then placed in line buffer 500 for eventual access by the DMA of system 10 for display on CRT monitor 96.

In system 10, the following components provide the operation and function herein described.