The 74HC166; 74HCT166 is an 8-bit serial or parallel-in/serial-out shift register. The device features a serial data input (DS), eight parallel data inputs (D0 to D7) and a serial output (Q7). When the parallel enable input (PE) is LOW, the data from D0 to D7 is loaded into the shift register on the next LOW-to-HIGH transition of the clock input (CP). WhenPEis HIGH, data enters the register serially at DS with each LOW-to-HIGH transition of CP. When the clock enable input (CE) is LOW data is shifted on the LOW-to-HIGH transitions of CP. A HIGH onCEdisables the CP input. Inputs include clamp diodes which enable the use of current limiting resistors to interface inputs to voltages in excess of VCC.