DESCRIPTION
The HEF4021B is an 8-bit static shift register (parallel-to-serial converter) with a synchronous serial data input (DS), a clock input (CP), an asynchronous active HIGH parallel load input (PL), eight asynchronous parallel data inputs (P0 to P7) and buffered parallel outputs from the last three stages (05 to O7).
Each register stage is a D-type master-slave flip-flop with a set direct/clear direct input. Information on P0 to P7 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 in the clock input makes the circuit highly tolerant to slower clock rise and fall times.