TC4021B is 8 stage parallel in/serial out shift register, which can be used also for serial in/serial out operations. In the case of parallel operation, the data of PARALLEL IN is input to each F/F asynchronously with CLOCK and the output is obtained. In the case of serial operations, each F/F is triggered by rising edge of CLOCK. (asynchronous parallel or synchronous serial input) Switching of PARALLEL operation and SERIAL operation is achieved by P/ S CONTROL input. When P/ S CONTROL input is “H”, PARALLEL operation is designated and when it is “L”, SERIAL operation is designated.