| 摘要 |
1,210,415. Cathode - ray tube displays. SPERRY RAND CORP. 12 Aug., 1968 [24 Aug., 1967], No. 38475/68. Addition to 1,108,401. Heading H4T. The "cursor" used to indicate the point of entry of a character in the character generation and display system of parent Specification is "painted" alternatively with a character, if one should occupy the position of the cursor, so that the "blinking" effect facilitates visual location of the latter. Referring to Fig. 1, the position the cursor is to occupy on the tube screen is set up in X register 4 and compared in comparator 10 with the instantaneous position of the beam as derived from M register 2, registers X and M operating as described in the main patent. When the two positions correspond an output is produced by comparator 12 and this is employed to control the alternate painting of the cursor and a character if one is to be reproduced at such position. As shown in Fig. 2, the output of the comparator 10 is supplied via two bi-stable toggles 46, 48 to a further bi-stable toggle 20 so that four output pulses from the comparator are required before circuit 20 can be toggled. When no character is to be painted at the cursor location zero signal on line 34 supplies an inhibiting input signal to AND gate 16 and, via inverter 36, an enabling signal to AND gate 16. The latter also receives the output from the comparator on line 12 and the output from the "1" side of toggle 20 on line 32 and thus supplies an output on line 44 which is effective via OR gate 26 to cause the cursor generator 30 (similar to Fig. 8 of the main patent) to "paint" the cursor. When, after four output pulses from the comparator, toggle 20 reverses and supplies an output from the "0" side on line 22, AND gate 14, enabled by the latter output and by the output on line 12, supplies an output to the cursor generator via OR gate 26 so that the cursor continues to be painted whilst there is no character to be reproduced at this position. When a character is to be reproduced, a signal on line 34 enables AND gate 18 while in response to the comparator output on line 12 and the output from toggle 20 on line 32 supplies an output on line 40 to the character generator 42 which operates to paint the character. The signal on line 34, however, operates via inverter 36 to inhibit AND gate 16 so that as toggle 20 reverses at every fourth output from the comparator AND gates 14 and 18 are alternately enabled and thus the cursor and the character are "painted" alternately so that with a scan repetition frequency of 60 c.h.s. the flicker rate of the character and cursor "painting" is 7¢ c.p.s. which is readily discernible by the eye. |
