The SN74HCS165 is a parallel- or serial-in, serial-out 8-bit shift register with Schmitt-trigger inputs.

This device has two modes of operation: load data, and shift data.

When the shift or load (SH/LD) input is held in the low state, the internal registers are loaded with data from the eight lettered inputs (A-H). This operation is asynchronous. In this state, the output (Q) will have the same state as the input H, while the inverted output (Q) will have the opposite state.

When the shift or load (SH/LD) input is held in the high state, the internal registers hold their current state until a clock pulse is received. On the rising edge of the clock (CLK) input, data from the serial input will be loaded into the first register, and the data in the internal registers will be shifted by one place. The last register will lose its value. The output (Q) will always be in the same state as the last register, and the inverted output (Q) will have the opposite state. The clock inhibit (CLK INH) input can be held high to prevent clock pulses from being detected. CLK and CLK INH are interchangable inputs.