Patent GB-1239920-A (GB)
Title: Improvements in or relating to symbol generators
Inventor: ELLIS ALFRED BRIAN EDWIN
IPC: G09G1/18
Filed: 1967-12-29
Abstract: 1,239,920. Alphanumeric displays. MARCONI CO. Ltd. 23 Sept., 1968 [29 Dec., 1967], No. 59166/67. Heading H4F. In a character generator a predetermined set of characters is recorded as an electrical charge pattern on one part of the target of a scan conversion storage arrangement, a corresponding set of digitally coded signals each signal of which specifies the position on the target of a different recorded character, is recorded on another part of the target and means are provided for reading- out any of the recorded digitally coded signals and for utilizing the output signals so derived to cause the corresponding charge pattern character to be scanned to develop video signals from which the character can be reproduced. The digitally coded signals may be produced by a keyboard or by a computer and a narrow-band channel is only required when, in manual operation, the keyboard or computer is remote from the rest of the apparatus. As shown in Fig. 1, a card CS bearing a set of characters (e.g. Alpha-Numeric) is scanned by a flying-spot scanner FSS to derive video signals which, with all of switches on contacts No. 1, are fed to the writing gun WG of a scan conversion storage tube SCT and recorded on the portion CT (see Fig. 2) of the target T. For this operation a normal line raster scan is produced by a scan generator ASG supplying the X and Y deflection circuits of the scanner FSS and with a suitable shift, the deflection coils WX, WY of the writing gun WG. The A switches (electronic switches in practice) are now moved to contacts No. 2 and on depressing the key on keyboard KT representative of a particular character (or the equivalent operation at a computer) a triggering pulse followed by a 6-bit binary coded signal is produced. The triggering pulse operates a deflection waveform generator MDG which supplies the deflection coils WX, WY with waveforms causing the writing beam to scan a line raster in the portion AT (Fig. 2) of the target each line being scanned in a series of steps, i.e. a short advance followed by a pause before the next short advance &c., the timing of the steps corresponding to the bit code time interval and during each group of six such steps the actual binary signals, which are fed to the writing gun WG, are recorded. When it is desired to display any of the recorded characters the deflection generator MDG which is triggered by operation of the appropriate key on KT causes the reading beam RG to be deflected via coils RX, RY and contacts 1 of switches B1, B2 to read-out the stored coded signals which are fed via an amplifier AM to a store BS. On the occurrence of a pulse from a generator PG the stored code signals are fed to the writing gun WG via contact 3 of switch A1 and re-recorded in the position initially occupied and are also fed to a digital-to-analogue signal converter which provides two outputs comprising analogue voltages corresponding to the X and Y co-ordinates of the the stored charge pattern character. Switches B now change to position 2 and the character bearing part AT of the target is scanned at the position occupied by the particular character by means of appropriate deflection waveforms from a generator CWG to produce video signals corresponding to the particular character for display. The generator CWG which is controlled by a pulse generator CRG synchronized by the pulse generator PG produces a line raster corresponding to the small area of the part AT occupied by a single character and to position this raster over such area the output of converter DAC is combined with the deflection waveforms as X and Y shift voltages. The video signals thus produced are fed via amplifier AM and contact 2 of switch B3 to a CRT display device MD the raster scan of which is produced by a deflection generator DDG controlled by the pulse generator CRG. In the operation of the arrangement all the A switches are ganged together and all occupy contacts the same number as are also the B switches and both sets of of switches comprising the electronic equivalent of the mechanical switches shown are operated by the outputs of respective timing devices MTC, FTC in a cyclic order which is described with reference to Figs. 5 and 6 (not shown). At the end of each cycle the target T is discharged by switch means EK.