The HEF4021B is an 8-bit static shift register (parallel-to-serial converter) with asynchronous serial data input (DS), a clock input (CP), an asynchronous active HIGH parallel load input (PL), eight asynchronous parallel data inputs (D0 to D7) and buffered parallel outputs from the last three stages (Q5 to Q7).
Each register stage is a D-type master-slave flip-flop with a set direct (SD) and clear direct (CD) input. Information on D0 to D7 is asynchronously loaded into the register while PL is HIGH, independent of CP and DS. When PL is LOW, data on DS is shifted into the first register position and all the data in the register is shifted one position to the right on the LOW-to-HIGH transition of CP. Schmitt trigger action makes the clock input highly tolerant of slower rise and fall times.
It operates over a recommended VDD power supply range of 3 V to 15 V referenced to VSS (usually ground). Unused inputs must be connected to VDD, VSS, or another input.
