The 74HC4520; 74HCT4520 are dual 4-bit internally synchronous binary counters with two clock inputs (nCP0 and nCP1). They have buffered outputs from all 4 bit positions (nQ0 to nQ3) and an asynchronous master reset input (nMR). The counter advances on the LOW-to-HIGH transition of nCP0 when nCP1 is HIGH. It also advances on the HIGH-to-LOW transition of nCP1 when nCP0 is LOW. Either nCP0 or nCP1 may be used as the clock input to the counter. 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. It enables the use of current limiting resistors to interface inputs to voltages in excess of V_CC.