Dual BCD counter

The HEF4518B is a dual 4-bit internally synchronous BCD counter. The counter has two clock inputs (CP0 and CP1 ), buffered outputs from all four bit positions (O0 to O3) and an asynchronous master reset input (MR). The counter advances on either the LOW to HIGH transition of the CP0 input if CP1 is HIGH or the HIGH to LOW transition of the CP1 input if CP0 is 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 (O0 to O3 = LOW) independent of CP0 and CP1. Schmitt-trigger action in the clock inputs makes the circuit highly tolerant to slower clock rise and fall times. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VDD.