DE2847419A1 - DISPLAY UNIT - Google Patents

Description

October 31, 1978 S / kn - 9245

GEC Computes Limited, Borehamwood, England

Display unit

The invention relates to a display unit in which a display surface is scanned in raster form and in which a character or other symbol is thereby generated on the display or visible surface will cause a change in the brightness of one or more selected portions of the raster line.

An example of such a cell-scanned display unit or display is a cathode ray tube which is constructed to be scanned in the manner of a television raster will. However, other forms of cellular scanned display units or viewing devices are also known, for example a series of light emitting diodes arranged to be electronically scanned, a screen, the scanned by a laser beam, or any display

909819/0759

surface, which is effectively a regular arrangement of display elements represents. Cell scanned display units can be used to provide an alphanumeric display, and in one form such a display is produced by storing digital representations of such alphanumeric characters and read out to form the display. Such a unit is satisfactory for common displays which the characters that make up the display, spaced positions along one or more precisely defined positions Ranks occupy, however, difficulties arise when the characters from such spaced positions to one another have to be relocated, for example if the characters are to overlap or in subscript or superscript To form indices against other characters. Similar difficulties arise when displaying other symbols, for example to form a mimic diagram.

The invention is based on the object of providing a display unit in which the above-mentioned difficulties are eliminated are.

According to the invention, this object is achieved by the subject matter of the main claim. Further refinements of the invention result from the subclaims.

The display unit has first data storage devices that are arranged such that opposite each of a plurality of raster lines or raster lines of the display there is a serially connected sequence of data with respect to the identity and grid line position of all characters or other symbols are stored on the origins of the relevant raster line, with data units of such a

909819/0759

serially connected sequence are stored at different locations in the first data storage device. A second Data storage device stores the addresses of the location in the first storage device with respect to each of the raster lines, on which a data unit (data word) of the serially connected data sequence is stored, so that the reading of the data sequence is facilitated. Furthermore, raster line storage devices are devices for writing information provided in digital form in the raster line memory, which characterizes a raster line, this information from derived from a plurality of data strings stored by the first data storage means relating to the characters or others Symbols is stored, which lead to the grid line in question. A device is used to output a video signal for controlling the display during a raster line, whereby the video signal is derived from information, which is stored by the raster line storage means.

Preferably, the origin of a character or other symbol is at the lower left corner of the character or symbol or the cell matrix which is occupied by the character or symbol. However, this is not essential and the Origin can be at the upper left corner of the character or symbol or the matrix of cells or any other easily identifiable In place at the cell matrix configuration.

The first data storage means can also store data relating to the character brightness value and the character type i.e. whether the character should appear light on a dark background (normal) or black on a light background (inverted). The first data storage device can also store data that

909819/0759

Have relation to whether a character is "constantly" or in intermittent "flashing or flashing" form should be present.

The following is a preferred embodiment of the invention Display unit for the description of further features explained with reference to the drawing. Show it:

La and Ib show a block diagram in a schematic representation from the display unit,

FIGS. 2 to 7 are diagrams for explaining the mode of operation of a data storage arrangement according to FIG. 1,

8 shows typical representations of the characters to be displayed,

9a shows a further typical representation of characters to be displayed,

FIG. 9b is a diagram for explaining FIG. 9a,

10a and 10b are diagrams for explaining the structure of the line memories according to Fig. 1,

Fig. Ha two overlapping characters, and

Fig. 11b is a diagram to explain how the data entry in the line store is done in these examples.

According to FIGS. La and lb, the display unit has a data memory transmission path 1, via which the to be displayed on the display surface of a display unit 2 or a display screen Data are kept from a data input memory. The display unit 2 is of a known type in which the display area is scanned in raster form and in which a symbol or character is generated on the display area that a change

909819/0769

in terms of brightness at selected portions of the raster lines, e.g., a cathode ray tube which is scanned in the form of a television grid. For the purpose of controlling the raster scan, the display unit 2 is provided with a Line and frame time base circuit, which is not shown in the drawings.

It should be noted that many of the connections represented by lines in Fig. La and Ib are actually multiple connections, i.e. connections consisting of a large number of lines, over which electrical signals are carried in parallel. The transmission route 1 illustrates such a multiple connection. To aid in the identification of the multiple connections, there are they are shown in the drawings by thicker lines than would otherwise be the case. Typical alphanumeric characters can are each formed in the display on a matrix of points, each consisting of eleven rows with nine points, where the rows of points coincide with one of the grid rows. Each character cell dot matrix has its origin at the lower one left corner.

The data to be displayed stored in the data input memory 3 are periodically transmitted via the transmission path 1 and a Buffer register and a memory controller 4 are transferred to a display data memory 5, which has a reference address memory 5 and an image memory address register 9. The image memory 8 sequentially leaves the thereby with regard to of each raster line to one or the other of a pair of line memories 1OA and 1OB, which in turn pass the data to a video generator 11 which is provided to generate a video signal which the display unit 2 controls.

909819/0759

According to FIG. 2, the reference address memory 6 has a storage location for each raster line, typically a total of 256, and each storage location is provided in such a way that it can store eleven data bits. Ten of the data bits P contain an image memory address, while the eleventh data bit V - if a "1" is set - indicates that the image memory address is a valid address, while if "0" is set it is indicated that no stored character is the particular raster line y has vertical coordinate. The pointer memory address register 7 is provided in such a way that it can store eight data bits and holds the current pointer memory address which is equal to the number of those raster lines Y which are processed in each case.

The image memory 8 has a storage space for each of a maximum Number of characters that are simultaneously represented by the unit 2, for example a total of 1024, and each memory location is arranged to store data bits as follows:

C 10 data bits which define the toe code - 7 data bits

Display mode - 3 data bits

(The 3 bits for the display mode each specify the brightness value of the character, the character type (i.e. normal or inverted) and whether the character should appear continuously or repeatedly, i.e. flashing).

X 9 data bits defining the X position code of the origin of the character (Typically the origin of a character can have any of 300 positions within a raster line consisting of 45 groups of eight dot positions, and six of the bits (X. g) specify the particular Group of eight points within which the origin occurs; the remaining three bits (X ₁ ") specify the position of the origin within such a group.

909819/0759

N 10 data bits define the image memory address of the next Character to be read when data is transferred to line memory 1OA or 103 (this is the connection, through which all characters whose origins have the same y-coordinate address are concatenated with one another, regardless of the order in which they occur in the memory 8).

V _n , 1 data bit which, in the "1" state, indicates that the connection address N is valid. When set to ¹¹ O ", it indicates the end of a chain.

From Fig. La it can be seen that the image memory 8 normally contains three RAMs 12, 13 and 14, each of the C, X and N (with \ Save bits (RAM = memory with direct access).

The image memory address register 9 is constructed in such a way that ten data bits are stored and the address N of the image memory location F, to which there is current access.

The way in which the data is written into the memory 5 under control of the clock signals which are sent by the controller are supplied, is explained below. It is assumed that the character data are character codes, display modes and X- and Y positions of the origin of each character and that these character data from the data input memory 3 via the Transmission line 1 were led to the memory controller 4. It is also assumed that there is no preceding character - if it was present - had an origin on the same grid cell Y as the characters related to the data that currently being treated. Depending on the Y coordinate of the first character arriving, the address register 7 is opened

909819/0759

the pointer memory address is set in the pointer address memory 6, which is equal to the number of the raster line Y. To this Point in time, the address register 9 stores the address of the next available memory location F in the image memory 8 (in the the first character CHl is to be set) and the data received from Memory 5 are stored as shown in FIG.

The valid data bit V _y in the memory 6 is read by the controller 4 and found to be ¹¹ O ", indicating that the character CH1 currently being processed is the first character originating on the raster line The address (Np ₁ ,,) of the image memory location (which is read from the address register 9) into which the first character CH1 is to be entered is then entered into the currently addressed memory location of the memory 6 and the valid data bit V _y is set to »Ί ^11. The identity (C _cm ) of the character CHl and the X position (X_ _H J its origin are stored in the memory 8 in

the location F _{OTT1 is} entered and V-, _TT , is set to zero. In OHl L-ill

Preparation for the next write operation in memory I. the address stored by the image memory address register is increased to! ^ "" .. + 1 and the resulting state of the

oil I

Memory 5 is shown in FIG. 3.

If a second character CH2, which has an origin on the same raster line Y as the character CH1, has to be entered into the memory 5, the address register 6 is reset to Y, while the address register 9 is set to the next available location N "_ in refers to the image memory 8 to which the second character CH2 is to be set (it is assumed that characters originating from other raster lines were entered between the input of the characters CH1 and CH2, so that Ν « _{Η2 is} not fN ^ + 1 is). The address of the

909819/0759

2847413

Image memory location N ... , which was previously placed in the pointer address memory location Y, is written to the next address part of the image memory location N ₀ and the bit \ T _UO for valid data is set. The address of the image storage location Npuo / at which the second character CH2 is to be entered is entered into the reference address memory 6 at location Y (in place of the previously stored address) and the bit Vy for valid data is then set to "1". The character CH2 is entered in the location N,. ,, _o and the address register 9 is set to move to the next available location Ν _ΓΗ? +1 in the image memory as shown in FIG.

After a further interval during which other characters that have their origin in other raster lines are transmitted from the inputs' junction memory 3, third and fourth characters, which have their origin on a specific line Y CH3, and CH4, transferred and similar to the characters CH1 and CH2. The final state of the various components of the display data memory 5 after transmission and storage is shown in FIG.

It can be seen that the arrangement of the data memory 5 described so far, all the necessary data in terms of by the unit 2 stores characters to be displayed at any time, this data as a plurality of serially connected Data sequences are organized, each of which has relation to all the characters that each originate on the sequence have the same grid line. The memory 5 retains this data for as long as the display requires and for delivery the display derives the video information for each successive raster scan from the multiple stored data sequences, which contribute to this raster line and is temporarily stored in

909819/0759

stored in the line memory 10A or 10B. The required Video signal to control the display unit 12 during each Raster scan is derived from the video information stored by line memory 10A or 10B like this mentioned above; one of the line memories 10A and 10B is read during each raster scan while the other Line memory is loaded and ready for the next raster scan.

The signals used to control the transfer of data from the Memory 5 in the line memories 10A and ΊΟΒ and for the derivation of the video signal are required are generated by a signal generator 30 which has a pulse source 16, to which five counting circuits 17 to 21 are connected. The pulses supplied by the counting circuit 17 to the counting circuit 18 have the frequency of occurrence of the points on the display surface of the unit 2, so that the circuit 18 as a point counter can be viewed. Circuits 18 and 19 operate in a similar manner to determine the number of point groups (each from consist of eight points) in a raster line, as well as the number of raster lines and are used to deliver signals Via paths 22 and 23, each group (in a raster line) and to characterize each raster line. The signals supplied via path 23 are actually used, to the address register 7 at the beginning of each sequence of writing the raster line data in the line memories 1OA and To address 1OB; it is to be remembered that everyone has space this register is uniquely identified with a special raster line.

The way in which the raster line Y, previously considered, is treated for the purpose of delivering the video signal,

909819/0769

is described below. However, it is believed that the Characters CHl and CH4 are the only stored characters that originate from the raster line in question. When the data is transferred to the line memory 1OA or 10B, the data related to the characters that have their origins on line Y will be in reverse order opposite to the order in which it is input, so that the data form a serially connected data sequence, as shown in FIG 7 is represented by dashed lines 15.

As has already been explained, the address register for the reference address memory 7 is set to the vertical address Y for the current display and the valid data bit V _y for the line Y in the reference address memory 6 is checked by the controller 4; it is determined that this bit is set to "1", which indicates that one or more characters CH originate on the Y line. The address N _{rH /} ^e ,, di- n ° memory location Y of the reference memory address is detected 7, is used to space the F_ _u. of the image memory 8 to

0114

read and the data bits C ",. are used to access RAM 24

0H4

address (which acts as a character generator) and the dot pattern that is generated in this way is set in the line memory 10A, for example, at the position indicated by the bits X _H. is displayed (at this point the data words or data units between the character generator 24 and the line memory 10A can be ignored).

The bit V _CHZf for valid data in the memory location F _CH ^, _ <Jas is assigned to ^the next image _{memory location address N CH3} in the memory 8, is then checked and it is determined that this bit is "1". The address register 9 is therefore set to the location address N _CR ", and the location F _CH3 is in the

909819/0759

Image memory 8 read; the data bits C, Y are used to place the corresponding dot pattern for the character CH3 in the correct place in the line memory 10A. On similar ones
Thus, the ^locations F ^ o unc '* γτπ * ^m image memory 8 are read in this order and the appropriate dot patterns for the characters CH2 and CH1 are placed in the correct locations in the line memory 10A. In this way, all of the data for characters originating on the Y line and serving for display in the Y line are transferred to the line memory 10A. If, however, the data bit V _CH1 for the character CHl at location F ^ is checked and identified as "O"
is detected, it indicates that the end of the serially connected data sequence has been reached.

Since each displayed character is in a cell that is "eleven raster lines" high, characters may be stored in memory at any time, these characters originating in eleven adjacent raster lines and which characters are required to contribute to each individual raster line display. Thus, the sequence described in the last two paragraphs becomes
repeated ten times to build up the necessary line data in the line memory 10A (or 103), the character generator 24 is controlled so that the signals generated thereby during each sequence in relation to the appropriate allocation of the in question
standing character for the respective raster line. For
for this purpose a buffer register 25 is arranged between the line counter 20 and the address register 27 and a counter 26 is provided to supply signals to the character generator 24 so that the series of character data read therefrom is selected. At the beginning of a read cycle from the memory 5 in relation to the raster line Y, the register 25 and the address register 7 for the reference address memory are set to Y + 10 (not to Y, as was previously assumed for the purpose of explanation) and the counter

909819/0759

is set to "O" so that the character generator 24 assumes the state to generate signals relating to the first row of each identified character. If the controller 4 detects a zero "address valid" -8it V in the image memory 8, which signifies the end of a sequence (or a zero "address valid" bit V _y in memory 6 if the image memory does not during the sequence was addressed), the content of the buffer register 25 is reduced by 1 and the content of the counter 26 is increased by 1 and the process described is repeated for the next sequence, etc. At the end of each sequence, the content of the buffer register 25 with the content of the line counter compared and - if the content of register 25 is greater than the content of counter 20 - the content of register 25 is decreased and that of counter 26 is increased, but these operations cease if the two contents are the same (since all Data for the raster line in question are then written into the line memories 10A or 10B).

As explained above, the two line memories 10A and 10B are used alternately to store data for successive Save raster lines of the display. Each of these memories contains a RAM which is arranged to store the 360 video elements (points) a single line as 45 bytes of eight bits each. The organization of this RAM is shown in Figs 10b, where FIG. 10a illustrates how the video elements (numbered 0 to 359, each consisting of one bit) are a complete line are divided into bytes; Fig. 10b shows how these elements are stored in a 45 × 48 matrix memory. When the relevant line data of a character is written into the memory 10A or 103, the position in the memory is at which it is stored determined by the X position code read from the image memory 8; the six bits X, "

909819/0759

specify the byte position at which the origin of the character occurs, the three bits X ₁ _ specify the position of the origin within the byte position.

According to Fig. Ib, the bits supplied in parallel by the character generator 24 for writing in the line memory 1OA or 1OB with respect to the characters are actually written in byte positions which are determined by signals which are determined by a byte address register 27 depending on the X- Position bits (X. _) are supplied; the character bits are positioned exactly by a logical shift circle 28. (as required by the X position bits X ₁ ″). Since there can be up to nine bits to define a character in a raster line, the character information written in the line memory 10A (or 103) does not generally correspond to a byte. As will be seen in the following, it is thus customary that part of the information is written into one byte location and the remainder into the next byte location, the address register 27 being incremented so that the above operation can be carried out.

The signal supplied via a line 29, which represents the digit with the least significance of the line count, the executed by the counter 20, the line memories 10A and 10B are used to control the mode of operation. This signal is first to control a read / write switch 31, which leads corresponding signals to the line memories 10a and 10B, secondly to Operation of an address switch 32 to provide the correct address signals to the memories and thirdly to control one Switch 33 is used, which determines the memory from which the raster line currently subject to a display is derived. The address switch 32 operates in such a way that when data is written into the line memory 10A (as an example) the memory is through

909819/0759

the signals supplied from the byte register is addressed, while subsequent bytes stored in the line memory 10B are read out under the control of signals supplied from the dot counter 19, these signals each representing such a byte , which is led in parallel by the switch 33. The operation for reading data from one of the memories 10A or 10B eliminates the data so that at the end of a line read the memory is empty and is ready to receive the next line data. The video generator 11 has a parallel-serial converter 34 to which the byte signals from the switch 33 are supplied and the converter 34 supplies a single signal which carries the required video information in series and this signal is synchronized with a pulse signal combined (which contains the image and line synchronization pulses in a known manner), which is generated by a generator 35 before it passes through an amplifier 3ό to the display unit 2.

As explained above, a character can be displayed by the display unit 2 can be displayed in different ways, which is specified by the display mode. Fig. 8 shows the letter H in the playback in normal and inverted form; in both cases the origin 44 is the character cell dot matrix at the lower left corner and can be anywhere in the 25ό χ 3 <5O matrix appear on the display area. Know a character in inverted Form is displayed, a signal from the Sildspeüier 8 to logic circuit 38 to effect the required inversion. Similarly, if on the display mode The image memory supplies the determining bit that indicates that a character is to be displayed in a repetitive, i.e. flashing, form a signal to a flash circuit 39; the character bits then begin

909819/0759

selectively to line memory 10A (or 10B) under control a signal generated by the counter 21 to arrive. If the Brightness of each character displayed is controlled (by the corresponding display mode bit) to one or two values it is necessary for the storage capacity of each of the line memories 1OA and 1OB (see description above), be duplicated (to store the relevant display mode bit); the video generator 11 must be modifiable, to control the amplitude video point signals, which are thereby fed in the required manner depending on the brightness value bit will.

From Figure 9a it can be seen that a single line scan makes contributions for multiple characters that have their origins 44 "on different raster lines. If the video data to be assembled in the line memory 10A or 10B for this line scan, the codes and data for all of these Characters contained in the memory 8 and read from the memory 8. As indicated above, this is supported by the Structure of the memory 8 and the memory 6 brought about, which together with the character generator 24 and the shift logic 28 the The required pattern of the video bits can be entered at the exact location in the line memory 10A (or! OB). From Fig. 9b is it can be seen that the video bits in line scan Y with respect to the second H are partly in byte X and partly in Byte X + 1 occur.

If a byte location in line memory is 1OA (or 10B) for the purpose of writing is addressed in a byte, the current content of this position is read and after the passage of a switch 41 (which is fed under the control of the via a line 29 Signal actuated to select the corresponding line memory

909819/0759

is) and a multiple-OR gate 42 (to which the signals from the shift logic 28 are also applied) are rewritten in the line memory at the same place. Consider two characters H and T arranged in an overlapping configuration with their dot pattern origins in bytes X and X + 1 (FIG. 11) and in particular the line scan indicated by an arrow, line 6 of the ¹¹ H "and contain the line 0 of ¹¹ T ", the following results: It is assumed that" H "and" T "are the first characters which are assembled, ie, assembled, in the line memory 10A (or 10B). If the dot pattern for line 6 of "H" occurs at the output of the shift logic 28, the line memory 10A (or 10B) is _{addressed by bits X. 9} , which characterizes the position of ¹¹ H "; this memory supplies 00000000 as outputs, The current content of the byte location X. The content of the byte X and the eight bits of the various dot pattern (OOOOOIOO), which contain four bits that contribute to the "H", are combined by the element 42 and are included in the byte X-place rewritten. The place of the byte X -f 1 is addressed next and the content of this place is read and combined by means of the element 42 with the eight bits of the shifted dot pattern (OOOIOOOO), which contains five bits that lead to " H "and the result is written into byte position X + 1.

The dot pattern for line 0 of "T" then appears at the output of the shift logic 28. At this point in time, the bits X. _, which identify the X position of the ""! "" Address (the X + I byte Digit in the line memory 10A (or 10B) and the content (00010000) ^S read, j combined by the element 42 with the eight bits of the shifted dot pattern (00111111); the last seven bits of this dot pattern are allotted to the "T" and the result is

909819 / 07S9

written in byte position X + 1. The byte address is then incremented and byte X + 1 (OOOOOOOO) read, combined with the shifted dot pattern (100000000), - the first two bits are assigned to the ¹¹ T "/ then the byte X + is written 1. In this way, the video pattern for the line scan is gradually built up by superposition.

For the purpose of adding other symbols, e.g. with a shorter line length, which can be assembled to form a facial expression or other diagram can be that described above Display unit can be modified by arranging another generator instead of or in addition to the character generator 24. This other generator stores the required symbol information and is in the same way as that through the memory 8 Generator 24 addressed; it may take the form of a RAM in which the information regarding the symbols to be displayed is present is inscribed in the advertisement.

It was believed that the operation of enrolling Data in the memory 8 and the reading of the data from the memory 8 take place at very different times; usually can the former operation during the fly-back periods of the display unit 2 are executed. In order for both operations to be carried out at the same time without any restriction on the number of stored items that can be changed Data are executed, two identical image memories can be provided, each with an assigned reference address memory to have. With this modification, the two image memories are used in an interlocking manner, one of which is memory is filled with precise data, while the other supplies the data for the current display.

909819/0759

Although it was assumed in the example described that each row of points of the character point matrix in the display coincides with a single raster line, the size of each point can be doubled in both the X and Y directions so that each Point is rendered on a pair of adjacent raster lines.

In addition, the memory 8 can be enlarged so that the memory 12 stores at each location the identity of a pair of characters which originate on the same raster line, while the memory 13 stores an additional bit at each location. This additional bit provides a step-on flag, which - if it is set to "1" - displays the second character of the pair one cell to the right to the first character, while - on "0" - aas second character the first character can overlap. This arrangement significantly increases the display capability of the unit for a simple increase in the storage capacity of the image memory 8.

The display unit according to the invention has a data memory in which the memory to be displayed as a plurality of associated data sequences are stored, each such sequence having reference to such characters that have their origin on the have the same grid line. The data memory contains an image memory with a multiplicity of storage locations at which the individual data words of the connected data sequence are stored are, a reference address memory with a separate memory location for each raster line, in each of these memory locations the address of an image storage location can be stored; there is also an address register for the reference address memory intended. The data stored at every point in the image memory provide the identity for a display to be displayed

909819/0759

Character, its position in a raster line and the address (if available) of the position in the image memory of the next Data word of the connected data. The video signals for the following raster lines are alternately derived from two line memories, one of which is in the read state while the other is being filled with data from the concatenated data sequences are obtained, this data being stored in a data memory, with respect to all those characters which contribute to the raster line in question.

909819/0759

Claims (8)

fcriw & Ua '2 8 A 7 4 1 r.-lRfi. WU '..! - r: -U; h9l ilil-ΐίΐ. \ Ζ ·:; - '^;; M f ^: ..- ii3l
6 ir'rcij ^. ·. ,, -. vi. hi. 1 October 31, 1978 S / kn - 9245 GEC Computers Limited, Borehamwood, England Claims Display unit, in which a display area according to the "type of a grid is scanned, characterized by a first storage device (! GA) for storing a serial link Data sequence relating to the identity and raster line position of characters or other symbols originating on the relevant Raster line for each of a multiplicity of raster lines, the data words of such a serial chained data sequence are stored in different storage locations by a second data storage device (TOB) for storage for each of the raster lines, the location address in the first memory device at which a data word of the data sequence is stored is, so that the reading of the data sequence is made easier, by a raster line memory device, means for writing information in digital form in said raster line memory means, said digital form denotes a raster line and the information is derived from a plurality of data sequences stored in the first data storage 909819/0759 device are stored in terms of characters or other symbols that contribute to the raster line in question, and by means for outputting a video signal for controlling the display during a raster line from the by the raster line storage means stored information. 2. Display unit according to claim 1, characterized in that the origin of a character or other symbol is defined on the lower left edge of the character or symbol or the cell matrix which is occupied by the character or symbol. 3. Display unit according to claim 1 or 2, characterized in that the first memory device has a plurality of memory locations which are each arranged in such a way that data can be stored which determine at least one character or symbol, the position of the origin of the relevant character or symbol on the Raster line, and the address of the memory location in the first data memory at which the next data word of the serially concatenated data sequence is stored which is related to the raster line in question. 4. Display unit according to one of claims 1 to 3, characterized in that that the second data storage device has a plurality of data storage locations, each of which is different Raster line are assigned. 5. Display unit according to at least one of the preceding claims, characterized in that the first data storage device is arranged to store data relating to the brightness value and in that the device is used for generating or deriving of the video signal is arranged so that this signal is controlled in accordance with the serenity value data. 9 0 9 819/0759 6. Display unit according to at least one of the preceding claims, characterized in that the first data storage device is provided for storing data relating to the display mode of a character or other symbol and that the video signal is controlled depending on this data. 7. Display unit according to at least one of the preceding claims, characterized in that the first data storage device is provided for storing data relating to whether a sign or other symbol is constant or flashing, intermittent form appears and that the video signal is controlled depending on this data. 8. Display unit according to at least one of the preceding claims ^ characterized in that the raster line memory device has two raster line memories which are arranged in such a way that they can be used alternately so that the video signal is derived from the information with regard to a raster line, which was previously written into one memory, while the information relating to the other raster line is in the other Memory is being written. 909819/0759