Patent GB-1234893-A (GB)
Title: A system for displaying graphic symbols
Inventor: LAVENIR JEAN-CLAUDE
IPC: G09G1/10
Filed: 1969-04-08
Abstract: 1,234,893. Cathode-ray tube displays. J.-C. LAVENIR, and J.-C. MERLIN. 8 April, 1969 [5 April, 1968], No. 17834/69. Heading H4T. In an arrangement for producing graphic symbols &c. on the screen of a cathode-ray tube by deflecting the beam by incremental steps in a desired one of a finite number of possible directions defined by binary digital (vector) words, predetermined combinations of successive pairs of the latter are utilized to define functions (e.g. beam blanking and unblanking) and do not produce beam deflections. Eight directions 0-7 (Fig. 1), specified by the corresponding binary number, are provided the steps length being about 1 mm. along the axes and 2 mm. along the diagonals and to produce traces of a desired length, the steps are repeated an appropriate number of times. Thus, in Fig. 2, the various limbs of the character R are produced by deflecting the beam in the directions indicated by the decimal numbers the number of times indicated by the decimal multiplier preceding the direction indicating number, i.e. limb ab is produced by eight step deflections in direction 2 and limb bc by three step deflections in direction 0. Portions of the trace which are not required for the production of a character, such as the " return " trace gf (=3x0), are blanked by providing a predetermined code formed by two consecutive digital words, a second, different, predetermined code also formed by two consecutive words being employed to produce unblanking of the beam. In the present case the transition 4-0 is employed for beam blanking and the transition 7-3 for beam unblanking and it is arranged that no symbol to be traced requires either transition for its production. Fig. 3 shows the succession of code words (shown in decimal notation) required to form the characters A to Z and the numerals 0 to 9, the successive words forming the blanking and unblanking codes being shown " boxed " thus |#40|, |#73|. Fig. 4 shows an application of the invention for use in a bank &c. to facilitate verification of signatures and the balance in an account (credit or otherwise) and to allow accounts to be credited or debited by a given amount. In operation, a keyboard 1 comprising letter keys, numeral keys 0 to 9, a +key, a - key and a " comma" key interrogates a time-shared computer system by sending binary coded information which may specify the name of an account and the amount with which the account is to be credited (plus key) or debited (minus key). The necessary arithmetic is performed by an Adder-Subtractor circuit 25 and the system responds by sending back to the interrogating position the amount of the new balance or if a debit balance, the word NO together with the appropriate signature from a register 23. This information which is sent back as three digit binary coded decimal words according to the scheme of Figs. 1, 2 and 3 is fed serially to a six-stage shift register 5, the first three stages of which after conversion to parallel form are supplied to a sequence detector 6 and are also utilized to control the deflection of the beam of tube 7 to trace the symbols via gates 16-18, binary-to-decimal decoder 9 and the elements 10 to 14 unless an inhibiting input is applied to the gates from a pulse generation 15. The outputs of the three final stages of register 5 are also converted to parallel form and also supplied to the sequence detector 6 together with the parallel outputs of the first three stages and when detector 6 detects the combination 4-0 it earths terminal 61 whilst when it detects the combination 7-3 a positive potential is applied to terminal 61. The condition of terminal 61 then operates via a bi-stable device 64 and inverter 65 to blank or unblank the beam via grid 71 when the combinations 4-0 or 7-3 respectively are detected by the sequence detector 6. Also on detection of either combination the variation in the condition of terminal 61 (earth or positive potential) controls a pulse generator 15 which then produces a pulse having a duration equal to that of two vector words ( = 6 binary digits) and this pulse prevents the transmission of the combination to the beam deflection circuitry so that traces corresponding to the (blanking) unblanking functions are not produced. The " end-ofpicture " is also represented by a predetermined transition code (not employed for symbol tracing) which occurs at terminal 62 and operates a signalling lamp 101 on the keyboard and a key 102 controlled by the operator modifies the potential of the target 72 to extinguish the display. A signal on terminal 63 is then employed to reset the various registers, converters and decoders of the system.