Patent GB-1294643-A (GB)
Title: Apparatus for synthesising characters
IPC: G09G1/10
Filed: 1970-05-04
Abstract: 1294643 Cathode-ray tube displays CASIO COMPUTER KK 4 May 1970 [2 May 1969 21370/70 Heading H4T [Also in Division G4] In an arrangement for producing'symbols &c. by the application of X-Y co-ordinate signals to deflection control means acting on the beam of a cathode-ray display tube (or on the deflection control means of an ink jet) the deflection between successive co-ordinate points defining the symbol is effected by a plurality of constant incremental steps which, in the case of arcuate, portions of symbols, connect a like plurality of points lying on a selected one of a number of predetermined (quadrant) curves. Thus, as shown in Fig. 1A, the numeral "5" which , in the form shown, is traced under the control of the X-Y deflection voltages shown in Figs. 1B and 1C by known circuit means, may be given the form shown in Fig. 2 by forming the strokes 6-7 and 7-8 as curved portions selected from the available arc segments R1 to R8 of Fig. 3, the segments R3 and R5 (see also Fig. 4) being utilized in this case. An approximation to each segment is produced by deflecting the beam (considering CRT operation) from the start point P0 (Fig. 5) between the points P1 to P7 and since the segments are "mirror images" of each other forming two basic patterns A, B, pattern A being formed by an increasing magnitude of the -X component steps the first step being zero, and a decreasing magnitude of the -Y component steps and pattern B by a decreasing -X component steps and an increasing -Y component steps (from zero) the segments may be specified by patterns A or B and the direction in which the component steps must be effected with respect to the reference start-co-ordinate point P0 considered as the centre of an Argand diagram, is whether positive -U(= up) or negative -D(= down). Figs. 6 and 7 show the general arrangement in which a diode matrix memory 600 (programmed as shown in Fig. 7 to produce the symbol "5") specifies the A or B pattern to a selection circuit 603 which controls UP Down X and Y counters 605, 606 to count in steps of I or II units (squares of Fig. 5) from an initial count preset (terminals PS) by the memory 600 and in a direction U or D also set by the memory unless inhibited by an input between terminals INH.  In operation, the memory is "scanned" by pulses t1-t m  from a shift register 604, the operation during the intervals t1 to t5, which control the production of the first five linear strokes of the symbol 5 (Fig. 4), commencing at the top right-hand portion -o, each stroke comprising seven elemental steps (counts) being conventional. On the occurrence of t6, however, the circuit operates to specify pattern B (segment R3), the -X counter is set to U and the -Y counter to D a count of 7 having being preset in the -X counter and a count of 14 in the -Y counter during the previous interval t5. The counters are then operated by clock pulses from pulse generator 601 and their outputs supplied to respective D-A converters (see Fig. 9) which supply analogue signals to the X and Y deflection means 609, 610. When segment R3 has been traced pattern A, (segment R5), is specified -and the counters are reset, the D (down) condition being required in each counter and during interval t7 the segment R5 is traced. The final linear stroke of the symbol is then produced during interval t8.