The ’HC165 and ’HCT165 are 8-bit parallel or serial-in shift registers with complementary serial outputs (Q₇ and Q\₇) available from the last stage. When the parallel load (PL\) input is LOW, parallel data from the D0 to D7 inputs are loaded into the register asynchronously. When the PL\ is HIGH, data enters the register serially at the DS input and shifts one place to the right (Q₀ → Q₁ → Q₂, etc.) with each positive-going clock transition. This feature allow parallel-to-serial converter expansion by typing the Q₇ output to the DS input of the succeeding device.

For predictable operation the LOW-to-HIGH transition of CE\ should only take place while CP is HIGH. Also, CP and CE\ should be LOW before the LOW-to-HIGH transition of PL to prevent shifting the data when PL\ goes HIGH.