74HC4017DB

The 74HC4017; 74HCT4017 is a 5-stage Johnson decade counter with 10 decoded outputs (Q0 to Q9), an output from the most significant flip-flop (Q5-9), two clock inputs (CP0 and CP1) and an overriding asynchronous master reset input (MR). The counter is advanced by either a LOW-to-HIGH transition at CP0 while CP1 is LOW or a HIGH-to-LOW transition at CP1 while CP0 is HIGH. When cascading counters, the Q5-9 output, which is LOW while the counter is in states 5, 6, 7, 8 and 9, can be used to drive the CP0 input of the next counter. A HIGH on MR resets the counter to zero (Q0 = Q5-9 = HIGH; Q1 to Q9 = LOW) independent of the clock inputs (CP0 and CP1). Automatic code correction of the counter is provided by an internal circuit: following any illegal code the counter returns to a proper counting mode within 11 clock pulses. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of V_CC.