Freescale Semiconductor - NXP

The HEF4520B is a dual 4-bit internally synchronous binary counter with two clock inputs (nCP0 and nCP1), buffered outputs from all four bit positions (nQ0 to nQ3) and an asynchronous master reset input (nMR). The counter advances on either the LOW-to-HIGH transition of nCP0 if nCP1 is HIGH or the HIGH-to-LOW transition of nCP1 if nCP0 is LOW. Either nCP0 or nCP1 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 nMR resets the counter (nQ0 to nQ3 = LOW) independent of nCP0 and nCP1. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VDD.