JPS55140972A - Coordinate value checking circuit - Google Patents

Abstract

PURPOSE: To avoid sending the reading data to the processor by deciding it as the erroneous data in case the continuous coordinate value is read mistakenly or the light pen gets out of the basement board, thus omitting the data check at the processor.

CONSTITUTION: Reading data 10 of the coordinate value is stored into the 1st register 11 via reading pulse 14. And data strobe pulse 20 is transmitted to the processor via AND gate circuit 19 in the case of the first data 10. Pulse 20 is then applied to the 2nd register 12 after the delay given by delay circuit 17 in the fixed time, and the data of register 11 is stored into register 12. At the same time, control circuit 16 which controls OR gate circuit 18 with pulse 14 used for the input is provided. And then the comparison is given at comparator 13 between the continuous coordinate value stored in registers 11 and 12. And in case the difference of the absolute value is within the fixed range, the logic is set up for circuit 18 to deliver pulse 20. While in case the light pen gets out of the basement board, the logic is not set up by the output of circuit 16 to inhibit the transmission of pulse 20.

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