74HCT166

The 74HCT166 is high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A.

The 74HCT166 is 8-bit shift registers which have a fully synchronous serial or parallel data entry selected byan active LOW parallel enable (PE) input. When PE is LOW one set-up time prior to the LOW-to-HIGH clock transition, parallel data is entered into the register. When PE is HIGH, data is entered into the internal bit position Q₀ from serial data input (D_s), and the remaining bits are shifted one place to the right (Q₀ ® Q₁ ® Q₂, etc.) with each positive-going clock transition. This feature allows parallel-to-serial converter expansion by tying the Q₇ output to the D_s input of the succeeding stage.

The clock input of the 74HCT166 is a gated-OR structure which allows one input to be used as an active LOW clock enable (CE) input. The pin assignment for the CP and CE inputs is arbitrary and can be reversed for layout convenience. The LOW-to-HIGH transition of input CE should only take place while CP is HIGH for predictable operation. A LOW on the master reset (MR) input overrides all other inputs and clears the register asynchronously, forcing all bit positions to a LOW state.