The HC166 and HCT166 8-bit shift register is fabricated with silicon gate CMOS technology. It possesses the
low power consumption of standard CMOS integrated circuits, and can operate at speeds comparable to the equivalent low power
The HCT166 is functionally and pin compatible with the standard LS166.
The 166 is an 8-bit shift register that has fully synchronous serial or parallel data entry selected by an active LOW
Parallel Enable (PE\) input. When the PE\ is LOW one setup time before 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 (DS),
and the remaining bits are shifted one place to the right (Q0 → Q1 → Q2, etc.) with each positive-going clock
transition. For expansion of the register in parallel to serial converters, the Q7 output is connected to the DS input
of the succeeding stage.
The clock input 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 CE\ input should only take place while the 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.
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