GB1336953A - Reversible counting device - Google Patents

Abstract

1336953 -Reversible counters BENDIX CORP 6 Dec 1971 [14 Dec 1970] 56568/71 Heading G4A A pulse counting system arranged to add pulses applied at 64 and subtract pulses applied at 66 comprises an input circuit feeding a counter 12 and including delay circuits so that it can accommodate two consecutive applied pulses whereby, when it is determined that the next pulses to be applied to the counter will cause the accumulated count to pass through zero, the signals necessary to change the counter 12 from incrementing to decrementing or vice versa can be generated before the counter actually reaches zero thus allowing counting at maximum speed. The counter 12 operating in binary coded decimal comprises several decades 20-26. Pulses applied at 30 are fed via an inverter 32 to the units stage 20; as each stage reaches a count of 9 or 1 depending on the counting direction it issues a signal at terminal U/D to condition a gate 34-38 so that the next pulse is applied as a carry pulse to the next stage. The direction in which the counter counts is determined by a signal applied to terminals MC froma line 28. The two input pulse trains at 64, 66 are added together by OR-gate 84 and fed to the input 30 of the counter 12. The signal on 28 which determines whether each individual pulse is to increment or decrement the counter 12 is derived from a gating unit 18 which issues a new signal for each input pulse to the OR-gate 84 and is also controlled by a sign flip-flop 74. When the latter is in the state indicating the count is positive the unit 18 issues signals to 28 causing pulses from 64 to increment the counter and pulses from 66 to decrement it. When the sign flip-flop changes over the signals have the opposite effect. A gating unit 40 provides an output whenever (a) the counter 12 is registering 1 and is conditioned to be decremented by the signal on 28 and (b) a pulse to be counted has passed a point 58. This output enables an AND gate 68 which sets the sign flip-flop 74 according to whether the next pulse arrives on line 64 or 66.