GB1449236A - Self-clocking punched tape reader - Google Patents

Abstract

1449236 Punched tape reader HONEYWELL INFORMATION SYSTEMS Ltd 31 Oct 1974 [1 Nov 1973] 50758/73 Heading G4M A reader for punched tape has for each data bit in a row two sensors RH1, RH2 sensing corresponding areas on the tape that are longitudinally displaced but overlapping. As shown there are two sets each having six sensors and the sensors from each set feed a respective OR gate G1, G2. Gate G1 via an inverter Il feeds a reset input of flip-flops SA1 which is set by a signal from gate G2 so that the flip flop is set for the period during which a hole is detected by any of the sensors RH1 and is reset when all the sensors RH2 detect no holes. The sensors also feed a comparator EQ1 producing a signal when the signals on the two lines 13, 14 are identical. Since some signals will rise later than others and some will fall earlier than others the pulse from EQ1 is shorter than that from SA1 and is wholly contained by that from SA1. Flip-flop SA1 and comparator EQ1 feed a one shot OS1 producing a short pulse passing the data from sensors RH2 via AND gate G4 and forming a strobe pulse STR. The inverted OS1 signal feeds a reset input of an error flip flop ER1 the set input of which receives the signal from flip-flop SA1. If two strobe signals are produced in a period in which only one should occur, i.e. if EQ1 goes true, false and true one shot OS1 produces two strobe pulses. At the end of the first strobe pulse ER1 is reset to enable AND gate G5 and the second strobe pulse passes gate G5 to produce a DST error signal. AND gate G6 is enabled by the set output of ER1 which is true for only a short period between the start of the SA1 signal and the end of the strobe signal OS1. if the comparator does not detect equality then ER1 is not reset and a signal on line ER1<SP>1</SP> enables an AND gate G6 which passes a signal at the end of the readout period.