NO842346L - VARIABLE LOADABLE CHARACTER GENERATOR. - Google Patents

Description

The present invention generally relates to data processing systems and more precisely to an apparatus and a method for generating the different types of character sets, including

ve several national language character sets.

The character generator is the means of translation from the character code assigned to a particular character to be displayed on the cathode ray tube to the dot pattern for the particular character in question. In order to achieve appropriate speeds, character generators are usually implemented in hardware, which uses a table look-up system with a table stored in a reserved storage device, usually a read memory/programmable read memory, where the character code acts as part of the address of the storage device. There are different methods of character generation. The applicant has not carried out any investigation of what is known in the area. However, in a recent ruling in a District Court for the District of Delaware concerning a "Cole Patent" litigation (U.S. 3 3^5 ^58, Master File Docket Number 78-198) the court's remarks include the following overview of the technology .

"An overview of the Technology"

"In designing a system to receive digitally encoded data and display it in decoded form on a cathode ray tube (CRT), there are certain parameters that must be taken into account. Among these are:

"1. The scan pattern type. The two types primarily considered here include one where the scan covers one character space at a time (a miniature raster scan pattern) and one where each scan line covers a horizontal section of each character in a row, the beam scans the full width of a CRT (television raster scanning pattern) screen." 2. The CRT type. The two main types are the one with memory, which can hold an image for minutes, and the type without memory (including those with a high demand), of which a TV tube is an example, which must be "refreshed" at a sufficient rate for that the image should appear continuous. M. Storage. In a system where a CRT is used without memory, (a storage device or memory is required, because the video signal is applied to the cathode ray tube a number of times per second.

However, the storage device can either be one that stores the character code before decoding, or one that stores the video bits produced by the transmission process. When the former is used, the system is sometimes referred to as an "on-the-fly" system to imply that video bits are applied to the input of the cathode ray tube as each bit is generated by the converter, as opposed to a system that involves storing the video bits.

"Each type of raster scanning pattern has its advantages

and disadvantages. An advantage of the miniature raster scan over the TV raster scan is that the character code can be presented at a lower speed with the same number of characters per row and number of rows per screen.

"The two main advantages of using a TV scan are the cost savings in the system's screen part (the cathode ray tube and deflection circuits) and the ability to superimpose signs on images or other video representations (such as maps, etc.). However, these advantages generally only become significant if you can operate at speeds at least equivalent to 'commercial' or 'entertainment' TV speeds. Then one can buy a mass-produced display system from stock relatively inexpensively or simply send messages to TV sets already in use for other purposes, and also mixing character signals with other video signals operating at commercial TV speeds At least the first advantage is lost, however, if the cost of producing video character signals at commercial TV speed exceeds the cost savings in the display part.

"As the CRT's beam scans, the beam's information-controlling on/off state must be synchronized with the beam scan. This applies whether the beam follows a TV scan pattern or a miniature scan pattern. However, if the TV scan pattern is to operate at commercial TV speeds or faster, the synchronization requirement means that the electronic components must work at speeds that were not available in the 1950s and too expensive to be commercial in the early 1960s.

"The encoded input data form must be translated into video data

for controlling the on/off state of the cathode ray tube beam,

as it sweeps in a mini-raster or TV raster scan.

The patent literature from the 1950s indicates translator units j in the form of digital circuits for converting from a 6-bit character code to a pulse train that will display a 5 x 7 character matrix on a cathode ray tube. This is described in US-PS 2,920,312 (Gordon) and US-PS No. 2,987,715 (Jones).

"Among the analog translator devices known in the 1950s was the monoscope character generator. The monoscope does not generally produce a train of 35 pulse positions of equal length, each of which can be on or off, and is therefore not generally associated with a display of character- matrix type. Instead, it receives the 6-bit character code and produces a pulse train, the pulse lengths of which correspond to the exact width of the character to be displayed at different positions along the character height. Physically, a monoscope is the small cathode ray tube, usually cylindrical in shape, which has .a target plate that is printed or stenciled with characters, rather than a screen. The beam is deflected to one particular character on the target plate in response to the received 6-bit character code, and then scans the character. In response to this scan, produces monoscope an output signal which is pulse train with pulse lengths or durations corresponding to the time the beam crosses the character This pulse train closely reproduces the character shape and consequently produces characters of far better quality than the hole from a 5 x 7 character matrix.

"All cathode ray tube character display systems that are

of interest here uses signal storage, so that the cathode ray tube screen can be 'refreshed' repeatedly. Thus, a full screen of character-representing signals (sometimes called a 'page') is stored and used repeatedly to 'refresh' the screen. The storage consists of one of two types. The first type involves storing the 6-bit character codes that are received. The codes can then be read out by the storage unit and converted into the video signal when the CRT is scanning. The second type of storage comprises converting the 6-bit character codes as they are received into corresponding video signals and then storing the video bits. The video bits can then be read out by the storage unit of the CRT as its beam scans. Although both of these storage solutions include the storage of codes and both co-

where are generally of a binary nature and represent characters, they can appropriately be termed 'character code storage' and 'video bit storage' respectively.

"The disadvantage of video bit storage is that it takes up more storage space, as one screen or page of 35-bit character matrix codes must be stored - while character code storage only requires one screen or page of 6-bit character codes. However, the advantage of video bit storage is that the character codes are only translated once, after which the video bits are stored and read out at the same time as a beam scan. The character codes must thus not be translated at the same time as each scan of a scan line and the translation must therefore not keep pace with the fast beam scan. Furthermore, video bit scanning is particularly suitable for variable positioning of the characters on the screen."

As mentioned above, the advantage of the raster scanning technique of character generation by digital techniques only becomes significant if it can be operated at speeds that at least correspond to commercial or entertainment television speeds. This requirement is satisfied by the known technique using read memory/programmable read memory to achieve the speed. This technique has the limitation that it requires a dedicated storage device for character generation. Thus, only one character set can be generated and additional character sets that include different formats, such as elite and pica, and also foreign characters require additional hardware in the form of other storage units/programmable storage units. This makes it necessary for the manufacturer to store a variety of these machine goods in order to be able to provide full service to customers all over the world.

What is thus needed is a character generator which is loadable instead of fixed (storage unit/programmable storage unit) so that several character sets can be provided with a single hardware design.

The present invention is to provide an improved character generator.

According to the invention, it is sought to provide an improved character generator for use with a computer terminal which uses a cathode ray tube (CRT) as a display screen.

It is further an object of the invention to provide

provide an improved character generator which is loadable instead of a fixed read memory 7programmable read memory, so that multiple character sets can be provided with a single hardware design.

The invention also intends to provide an improved character generator that utilizes a minimum of hardware in order for the character generator to be rechargeable.

These and other purposes of the invention will be apparent from the following description in connection with the drawing.

The rechargeable character generator according to the invention

replaces the read storage/programmable read storage device with a direct storage, which uses 2K x 8 direct storage units, a 4 K

x 8 storage unit, 4 MUX chips and a Motorola 6845 CRT control unit with various registers.

80 characters are used horizontally and 12 scanning lines vertically per string of characters. A character code is read out from the computer display storage device for each character position in each scan line. Each time a new character is read out from the display storage unit, the character code is used as part of the address used to address the direct storage which acts as a character generator. The rest of the address for the character generator is taken from the scan line number. The address consists of 12 bits with 8 bits of higher order comprising the character code and 4 bits of lower order comprising the scan line number. As each scan line is scanned over the 80 character positions, an appropriate proportion of the character will appear at each character time and after a total of 12 scan lines have been completed, the 80 characters are displayed on the screen.

The construction of the apparatus according to the present invention and its operation can best be understood in the light of the following, detailed description with reference to the drawing, where

fig. IA and IB reproduce known methods for generating characters on a cathode ray tube (CRT) using video signals,

fig. 2 is a block diagram of the known method

for generating characters on a CRT using digital signals,

fig. 3 is a schematic representation of the addressing system according to the invention for generating characters on a CRT by

use of video signals,

fig. 4 is a high-level logic block core of the invention,

fig. 5 is a detailed logic block diagram of the CRT control unit and the MUXes according to the invention,

fig. 6 is a detailed logic block kernel of the transmitter-receiver units to/from the microprocessor, the image surface instruction buffer and the image surface data buffer according to the invention,

fig. 7 is a detailed logic block diagram showing the character generator and various storage registers and shift registers,

fig. 8 shows a typical organization of data in the image surface buffer direct stores,

fig. 9 shows typical values used for the start address and number of scan line parameters for sixteen rounds of a series of .

In order to understand the present invention, it is necessary to know how an image is formed on the cathode ray tube for a TV set. The image is formed by an electron beam that illuminates different points on the screen's phosphor coating as it scans the area where the image is to be displayed. Normally, the beam scans one horizontal line at a time, starting at the top of the screen and moving in sequence down the screen to its bottom. This scanning pattern, in which the beam is moved across the entire width of the cathode ray tube screen before scanning a new horizontal line, is referred to as the television raster scanning pattern. By using a digital video control signal for correct control of the intensity of the beam as it crosses the screen, the beam can be used to form a recognizable message or image. Due to the speed of the beam, its movement cannot be detected with the naked eye.

Each member of a character set can be represented by a set of points in a rectangular matrix that has fixed dimensions (e.g. 5 points width and 7 points height, or as in the present invention, 7 points depth and 9 points height). The character is displayed on the CRT screen in a character space that includes the character's dot matrix and additional blank spaces to separate the characters on the screen (eg 9 points wide by 12 scan lines high). Two such neighboring character spaces are shown in fig. IA, which reproduces the known technology. As the beam moves across the screen in a scan line, the data processing codes for each of the characters to be written in a row across the screen are supplied in turn from a storage unit to a decoder or "character generator". As shown in fig. 2, which also reproduces known technology, clock and control circuits form counting signals, which represent the scan line of the raster and the point position along the scan line. Character code information, the scan line count signal and the dot position count signal are applied to the character generator, digital-to-video generator 201, which converts the signals to a serial 2-level output. The output signal is applied to the television monitoring circuit 202 as a video signal. A digital level of the signal corresponds to a dot and rotates the electron beam to write a dot on the television screen. The second digital level corresponds to the absence of a dot and leaves the electron beam turned off, so that no dot is written. The points formed in this way, as the electron beam moves along a scanning line, correspond to the points in the relevant horizontal section of each character to be displayed in the character string. In fig. IA, points 103-105 (for the character "A") and points 106-109 (for the character "B") will thus be illuminated in turn when the electron beam is moved along the top scanning line. The timing and control circuits in fig. 2 also provides horizontal and vertical drive pulses to the monitor 202 to synchronize the scanning motion of the beam with the video signal generated as discussed above.

After a scan line is completed, the electron beam returns to the output side of the screen (but one position down due to the vertical sweep) to begin the next scan line. The sequential imprinting of character codes, scan line counting and point position counting is then repeated. This time, the video signals are generated for the next bit section of each character in the row.

After the correct number of scan lines (eg 8 or 12) are "written" on the screen, a full string of characters is complete. The entire row is written on the screen, one scan line at a time, from top to bottom.

The additional strings of characters that form the message

to be displayed on the screen is written in a corresponding way. After the entire screen has been scanned, the procedure is repeated at a rate of 60 times per second. second for "refreshing" the screen and for forming an image that the human eye perceives as a continuous, non-flickering image.

In fig. IB an example of the translation of the code for the character "1" to be displayed on the screen is shown. It should be noted that if the binary codes used to identify the various characters were applied directly to the cathode ray tube, the pattern on the screen would generally not be recognizable. Thus, the 6-bit code 000111 could represent a number "7", but would appear as 3 dark dots, followed by 3 light dots, or vice versa. It is therefore necessary to translate the 6-bit binary code into a video signal which will represent a normal-looking character. To see how this is done, refer to fig. IB, illustrating code to the pattern translation for the number "1". It should be noted that the video code for the first scan line is 00100 and that the video signal representing this code is a pulse in the position where the dot is to appear. Similarly, for scan line two, the video code is 01100, so a video signal representing this video code is two pulses that cause two dots to appear on scan line two. (When the entire scan is complete, the number "1" appears on the screen.)

In fig. 3, one character is shown in a row in a column. There are 80 such character columns on the screen and there are 25 character rows; 2000 characters can thus be generated on the page or screen. Fig. 3 shows how the letter "A" would be formed within the boundaries 301 to 302, when all 12 raster lines comprising a string of characters have been completed. (It should be noted that 9 raster lines are used for character generation, while 3 are added as spacing between character rows.)

To obtain this character (which may be part of a message), it must first be stored in a storage unit or buffer 7, which is shown in fig. 4. In order for this character to be written on the screen, it must be generated by the character generator 14. The character generator stores different standard characters at different addresses which can be used to generate the characters in any message on the screen and which are stored in the buffer 7 as previously discussed. The pattern stored in the character generator 14 is addressed using the character's code in the message as part of the address. In the present case, the hexadecimal code for "A" is 041, while the decimal code is 65. The address of the letter "A" will therefore be 65 x 16 for the first raster line and (65 x 16) +1 for the second raster line, etc. As each raster line advances forward across the screen, the patterns of different characters in the message are similarly addressed with their codes and a portion of each is generated, until a full string of characters is generated with 9 consecutive raster lines.

In fig. 4, a high-level logic block core of the invention is shown. Two data buses, a 16-bit address bus 1 and an 8-bit data bus 2, are coupled to a commercially available Motorola 6809 microprocessor 20. Controlled by the microprocessor 20, the microSystem 6/10 communicates the system (not shown) with the terminal, of which the invention forms part, via the address and data buses 1, 2. Two commercially available 6116 direct storage devices 7 and 8 are connected to the 8-bit data bus 2 via commercially available 74LS245 transmitter-receiver units 9 and 10. The transmitter-receiver units 9 and 10 can send data in both directions, from the data bus to the direct storage or from the direct storage to the data bus. Data is entered into the direct storage 7 or 8 at addresses controlled by the microprocessor 20, via the address bus 1. The selection of the direct storage 7 or 8 where data or image attributes are to be stored takes place via the bottom bit of address bus 1 via logic not shown . When a message is to be written on the cathode ray tube's screen (not shown), data (ie the message) is consequently written into the direct storage 7 via the transmitter-receiver unit 10 at addresses provided by the microprocessor 20. In a similar manner, image attributes (e.g. underline, blinking, etc.) are written into the direct storage 8 via the data transmitter-receiver unit 9. To write to the CRT screen (not shown), each character is broken up, as the scan line grows across the screen (not shown), as discussed above. Controlled by the CRT control unit, CRTC3, each character in the message is then addressed and read out to register 11.

Similarly, each attribute corresponding to a given character is simultaneously read out in register 12. For any character in a message temporarily stored in register 11, a full address, consisting of 8 high-order bits (as in reality represents the character code) and 4 low-order bits (which represent the scan lines, and which count 12 different scan lines 0-11), presented to the character generator 14. This (14) comprises two commercially available 6ll6 direct memories, which store a set of character patterns of which preferably distinctive type that can be addressed by the address formed by concatenating the character code with a scan line code as discussed above. As each separate scan line of a CRT display (not shown) advances through 80 character time frames, a portion of each character is written in each time frame on each scan line, as indicated at each time frame by the character temporarily stored in register 11 for the particular time frame. The scan line address will cycle from 0 to 11, and when 12 complete scan lines are done on the screen, 80 characters will be completed on the screen as a row. Shift register 15 which is connected to character generator 14 is the device for converting parallel data into serial data.

The invention is based on the fact that the attribute for a certain character arrives on the screen (not shown) exactly at the same time as the character arrives. This is achieved by storing character data in the screen data buffer and attribute data in the screen attribute buffer. As each address is presented to the display data buffer and the display attribute buffer, the character being addressed is placed in register 11 and the attribute being addressed is placed in register 12. Thus, the character code and the attribute code are available to the control logic for writing to the screen at the same time. As both the character information and the tribute information are available exactly at the same time, very precise timing and a clear image on the screen will thus be achieved.

It will now be shown that the invention provides an option for charging the character generator direct storage 14 in fig. 4 with a minimum of additional hardware compared to that required for the character generation function. The core of the invention lies in the addition of a single register 13 according to fig.

4 for creating a path for the data to be written into the character generator 13a together with a character generator charging rocker 17 and assigned control element 18 according to fig. 7. When this flip-flop is set to the character generator charge state, the character generator direct memory is set to write mode, and the above-mentioned three-level output of register 13 is opened, so that the contents of register 13 are written into the direct memory 14 on each character clock cycle , as long as this mode remains activated. The address where data is written is the 12-step address consisting of 4 scan line steps from CRTC 3 and the 8 steps from register 11, in the same way as when the direct memory 14 is used in its normal character generation function. It should also be noted that the register 11 is fed by the "data" half of the screen buffer direct storage 73, while the register 13 containing the data to be written is fed by the "attribute" half of the screen buffer direct storage 8.

What now remains is to show that there is a combination of "loading" of the screen data/attribute direct stores and a programming - or in reality - a set of programming of the CRT 3, as in connection with the load mode the hardware discussed above will cause the desired table to be fed into the character generator 14. The general strategy used is to load the "attribute" side of the screen buffer with the screen patterns and to load the "data" side of the screen buffer with the internal code normally used to invoke the associated patterns. These patterns are 12 scan lines high in the present case, but to simplify the addressing of the character generator direct storage 14, the patterns are assigned to blocks of 16 sequence locations. This enables an implementation where the address is simply the concatenation of the character code with the scan line number. Since the display buffer data and attribute direct stores contain 2048 ;(;2K) locations, there is room for 2048/16 = 128 patterns in a "load" of the data/attribute direct store. This is half of the 256 patterns that are desired to be fed into the character generator, so that the procedure must be split into two phases. The division would like to take place according to the internal code set with the first 128 codes handled in the first phase and the remaining 128 codes handled in the second phase. The description below deals with the processing of one of these phases, taking into account that the only difference between the two phases lies in the values of the data that are loaded into the data and attribute direct stores 7 and 8.

At the beginning of each phase, the screen attribute and data buffers are loaded with 128 patterns or the internal codes for the same, as the codes are repeated 16 times. The details of the arrangement of this data in the buffer direct stores are controlled by the operation of CRTC 3, which will be discussed now.

The CRTC 3 can be loaded with specific parameters, which will then control the unit's operation. Among these parameters, the following are of interest for the present context.

Number of characters per row

Number of scanning lines per string of characters

Number of character strings

The start address of the screen buffer

One purpose of the CRTC unit is to generate the correct sequence of addresses to the screen buffer to enable display of the patterns associated with the codes therein, while generating scan line numbers which act as part of the character generator address, as explained above . Another purpose of the CRTC device is to provide easy scrolling by having the beginning of the screen correspond to a random location in the screen buffer, hence the start address parameter.

The operation of the CRTC consists of sending out a sequence of screen buffer addresses and scan line numbers (as well as synchronization pulses, which are not discussed here). In particular, the transmitted sequence consists of a linear sequence of screen buffer addresses, starting with the screen buffer start address, where the length of the sequence is equal to the number of characters per row parameter, while the transmitted scan line count is kept at NULL. After an appropriate synchronization interval, this identical sequence of screen buffer addresses is repeated, while the transmitted scan line number is held at the value ONE. This process is repeated the number of times specified by the parameter: number of scanning lines per string of characters. After this, the entire process is repeated with the next set of screen buffer addresses in the sequence, and this iteration level is repeated, until the number of repetitions corresponds to the parameter number of character strings.

For a display of 80 characters per line, with 12 scanning lines per string of characters and 25 strings of characters, the sequence will thus consist of the first 80 addresses (starting with the screen buffer start address) where the scan line number is kept equal to NULL, followed by the same first 80 addresses with the scan line number kept equal to ONE, etc., until the scan line number is 11. the other 80 addresses generated 12 times, etc., until the 25 set of 80 addresses is finally generated 12 times (with the scan line numbers varying between 0 and 11 at each repetition of the same set of addresses).

We will now assume the following example to illustrate the loading of the character generator. The following imaginary "parameters" are loaded into the CRTC unit to control its operation during the charging function:

Number of characters per row = 128

Number of character strings = 1

Number of scanning lines per character string = variable and Screenbuffer start address = variable

Fig. 8 represents the organization of data in the screen buffer direct stores 7 and 8. The left half of each column represents the contents of "data" buffer 7, while the right half represents the contents of "attribute" buffer 8. The digits at the top represent the number of character patterns that to be loaded, while the digits along the left margin show the scale of addresses used for each scan line. The case shown in fig. 8 applies to the first phase of pattern loading, i.e. for character codes 0-127. Thus, as illustrated, the contents of the data buffer (left half of each column) comprise this scale of character code numbers in sequence, repeated 16 times. The designation "Pa.b"

(where "a" and "b" are numbers), shown for the contents of the right half of the columns indicate the binary representation of scan line "b" of the pattern for that character. whose code is "a". If we use the example in fig. 33 thus means that if the character code for "A" is 65 (what it is in ASCII), then P65.O = 0, P65.I = 16 (00010000 binary), P65.2 = 40 (00101000 binary), etc.

The correct pattern, organized as above, is loaded into the screen buffer by means of an appropriate program stored in the 6809 u P 20 at the start of each phase.

Now the operation of the charging algorithm will be described. Due to limitations resulting from the normal functioning of the CRTC unit, the process for one phase must be divided into 16 rounds. For each round, the CRTC unit is programmed as described below, then the character generator is brought into charging mode, until the entire CRTC sequence is sent. (This is determined by monitoring in a manner not shown here by listening to the vertical sync signal sent by the CRTC at the end of each complete sequence that the unit generates.) For completeness and simplicity, the loading of patterns with the full scale of 16 scan lines and it is noted that an improvement in loading time would be achieved by loading only those scan lines that are actually used for the image.

Fig. 9 shows the values used for the start address and number of scan line parameters for each of the 16 sweeps. It appears that the start address in the first sweep is set to the address that corresponds to the beginning of the last line in fig.

8, as this is the area where the 15 sections of scan lines for the character pattern are stored. The CRTC unit will in turn traverse this series of addresses 16 times, while the scan line number increments from 0 to 15. As the "data" halves of each location simply contain the sequence 0-127 and as this, together with the scan line number, forms the address of the character generator direct storage 14, this means that the scan line 15 patterns (right halves of the last row in fig.

8) will be written 16 times into the character generator 14. The first fifteen of these iterations are not desired, but the sixteenth loads the scan line 15 pattern information into the correct locations. In the second sweep, the start address is set to 1792 (second to last row in Fig. 8), but this time the number of scan lines is programmed for 15. This means that the scan line number output from the CRTC in this sweep will only range from 0 to 14, as that the scanning line's 15 pattern information, which was loaded in the first sweep, remains intact. Also in this sweep, only the last iteration (fifteen this time) through the 128 specified addresses in the screen buffer is fruitful. This is how the process continues and moves up a row in fig. 8 at a time, while the number of scan lines parameter is reduced by one, until the last (sixteenth) sweep<:>where we finally have a case that is 100% efficient; namely scanning once of the first 128 locations. At this point, half the character generator appropriate for the running phase is fully charged.

In fig. 5j 6 and 7 show detailed logical block diagrams for the invention as shown in fig. 4. It should be noted that elements in fig. 536 or 7 which correspond to corresponding elements in fig. 4 are identified with the same reference number. The character generator in fig. 4, which is denoted by 14, is thus also given the reference number 14 in fig. 7.

In fig. 6 it can be seen that screen data buffer 7 and screen attribute buffer 8 are connected together to form screen buffer 2K x 16. Data from 8-bit data bus 2, shown in fig. 4, data bus stages DBUS00-DBUS07 are applied to both transmitter-receiver units 9 and 10. The screen-buffer data signals SBDATO-SBDAT7 on transceiver unit 10 are applied to the SBDATO-SBDAT7 terminals of screen data buffer 7, when data is sent from the bus for to be written into screen data buffer 7. Conversely, data from screen data buffer 7 can be read out into bus 2 via receiver 10. Similarly, data representing attributes can be written into or read out of screen attribute buffer 8 and to or from bus 2 via the data bus terminals DBUS00-DBUS07 and Screen Buffer Attribute Terminals SBAT0-SBAT7 for Transceiver Unit 9-When transferring information to or from Screen Buffer Storage Units 7 and 8, it is sent to or from locations addressed by signals on terminals SBAD09-SBAD19. In addition, the write signal WESBAT or WESBOT for display attribute buffer 8 or display data buffer 7 must be true. This technique of using special write signals for selecting one or the other storage device allows the screen data buffer to be stored in one storage device set, while the screen buffer attributes are stored in another storage device set.

When it is desired to generate a character, the information in screen data buffer 7 or 8 is read out into registers 11 and 12 synchronously with the scan line time intervals. It will thus be seen that screen buffer data on terminals SBDATO-SBDAT7 will be printed on the SBDATO-SBDAT7 terminals for register 11. In a similar way, data from screen attribute buffer 8 will be printed on register 12. The information in register 11 is e.g. the character code required for the specified time interval. This character code is printed on the CC0DE0-CC0DE7 terminals of the character generator 14. In addition, the raster scan line address signals on the terminals RASTR1-RASTR4 of the CRT control unit 3 are printed on the character generator 14<*>on the raster scan line address terminals RASTR1-RASTR4 of the character generator 14. Consequently, the character generator 14, when the raster scan lines 0-11 are addressed and when each character is presented to the character generator synchronously with the scan line time intervals, decode a portion of the character and generate video outputs at terminals VIDD00-VIDD07 of the shift registers 15 on sheet 3 of FIG. 7. These signals are introduced in parallel and shift-out signals serially on terminal VIDOUT.

In fig. 5 it can be seen that the CRT control unit (CRTC) 3 generates all timing for screen display. It consists of the screen buffer address sequence sent on terminals CRTA09-CRTA19, the raster scan line number sequence sent on terminals RASTR1-RASTR4, as well as the horizontal and vertical synchronizing signals HSYNC1 and VSYNC2 and the display enable signal DISPLY. CRTC 3 can be "programmed", i.e. loaded with control parameters by applying the signals UDATA0-UDATA7 from data bus 2 to the unit's data terminals and applying appropriate control signals, such as UBUSRD PHAS.E, ABUS18 and CRTCCS. The multiplexers (MUX) 6 shall select an address for the screen buffer direct stores, either from CRTC 3 or from address bus 1. The former case is selected during (part of) each display character time to enable reading of the coded display data and attributes ; the latter case is selected under the control of the microprocessor 20, when it is made to write in or read out of the screen buffer in order to have the information to be displayed correctly stored in the screen buffer. (Specifications for the control units, such as the CRT control unit, are found in the Motorola Semi-conductor Catalog beginning at 4-457; while specifications for other elements are found in the Texas Instrument TTL Data Book for Design Engineers, second edition.)

When the invention has now been described so that an ordinary expert in the field can use it without too much experimentation, experts will understand that a number of variations and modifications can be carried out to produce the mentioned invention within the spirit and framework of the requirements. Thus, some of the machined board and/or steps can be changed or replaced with other machine equipment and/or other steps, which will give the same result and fall within the scope of the invention, which is exclusively considered to be limited by the scope of the subsequent claims.

Claims (7)

1. Device with a rechargeable character generator that has a character and attribute generation mode (e.g. blinking, underlining) and a character and attribute charging mode and includes a system clock, where the rechargeable character generator is charged with digital signals in each clock cycle or during charging mode :various characters and attributes, where the character generator in sequence utilizes a pre-selected character from the said characters to generate alphanumeric characters, characterized in that the device comprises (a) a character generator (14) for digital generation of selected characters using the digital signals, (b) a first register (13), which is connected to the character generator (14) for creating a path for the characters to be written into the character generator, (c) a flip-flop (17) which is connected to the character generator and to said first register so that the contents of said first register can be written into the character generator and (d) a control device (18), which is connected to the rocker for controlling the charging of the character generator with the contents of waited for the first register. 2. Device as specified in claim 1, characterized in that it comprises an addressing device, which is connected to the character generator for providing addresses indicating where data is to be written into the rechargeable character generator device. 3. Device as stated in claim 2, characterized by a second register (1,8) for loading data into the first register, the characters being written in the character generator. 4. Device as stated in claim 33, characterized in that the second register comprises two registers, a data register (1) for storing data and an attribute register (8) for storing attributes. 5. Device as specified in claim 4, characterized in that it comprises a screen data buffer unit, which is connected to the data register for storing data and an attribute data buffer unit which is connected to the attribute register for storing attributes, i.e. exclamation marks, underlining etc. 6. Data processing system, where data is processed in the form of binary, digital character codes and where data is presented in the form of character images, generated by binary, digital image patterns, where each special image pattern corresponds to each special character code, where the system comprises an addressable storage unit (14) to hold a majority of said image patterns, and where the addresses of the character images to be displayed when the system is operated in display mode, are imprinted on said storage unit, so that the image patterns that are thus addressed are read out by the storage unit for use of the display unit; where the system further comprises an addressable first buffer (7) to hold the character codes whose character images are to be displayed and an addressable, second buffer (8) to hold attribute codes for the images to be displayed, and where in the display mode addresses are effectively and simultaneously sent to the first and second buffer to cause reading of the addressed character codes and corresponding attribute codes, where each character code after reading from said first buffer is imprinted as an address element on the address storage unit, so that the image pattern addressed by said read out character code and the simultaneously read out attribute code is made available for efficient, simultaneous utilization of the display unit, characterized by an improvement to enable different character sets (fonts) to be displayed for said character codes by loading the addressable storage unit with the different image patterns for a particular font, creating a controllable path (13) between said second buffer (8) and it addressable storage unit (14) for enabling transfer of the contents of said second buffer to said addressable storage unit; means (6,9) for loading the second buffer (8) with a plurality of image patterns of a particular font; means (6, 10) for loading character codes into the first buffer (7), which character codes are stored in locations in the first buffer, the addresses of which are the same as the addresses of corresponding image patterns held in the second buffer (8); means (3,6) for simultaneously imprinting a sequence of addresses on first and second buffers to enable simultaneous reading from them of the stored character codes and character images; means (17) for enabling each image pattern readout from the second buffer to be stored in the addressable storage unit at locations whose addresses are provided by the character code simultaneously read out from the first buffer. 7. Data processing system as set forth in claim 7, characterized by a device (20) which selectively controls said system for operation in said display mode or in image pattern storage modej where the devices for imprinting said sequence of addresses and said devices for opening said controllable path in picture pattern charging mode is opened for operation.