The HEF4520B is a dual 4-bit internally synchronous binary counter. The counter has an active HIGH clock input (CP0) and an active LOW clock input (CP1), buffered outputs from all four bit positions (O0to O3) and an active HIGH overriding asynchronous master reset input (MR).
The counter advances on either the LOW to HIGH transition of the CP0input if CP1is HIGH or the HIGH to LOW transition of the CP1 input if CP0is low. Either CP0 or CP1 may be used as the clock input to the counter and the other clock input may be used as a clock enable input. A HIGH on MR resets the counter (O0to O3= LOW) independent of CP0,CP1. Schmitt-trigger action in the clock input makes the circuit highly tolerant to slower clock rise and fall times.