The 74HC166 are high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). they’re specified in compliance with JEDEC standard no. 7A. The 74HCT166 are 8-bit shift registers which have a totally synchronous serial or parallel data entry selected by an active LOW parallel enable (PE) input. When PE remain LOW one set-up time prior to the LOW-to-HIGH clock transition, parallel data entered into the register. When PE is HIGH, data entered into the interior bit position Q0 from serial data input (Ds). And therefore the remaining bits shifted one place to the proper (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 Ds input of the succeeding stage. The clock input may be a gated-OR structure allowing one input to used as a lively LOW clock enable (CE) input. The pin assignment for the CP and CE inputs remains arbitrary and reversed for layout convenience. The LOW-to-HIGH transition of input CE occur 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 coffee state. Inputs include clamp diodes enabling the utilization of current limiting resistors to interface inputs to voltages in more than VCC
In Parallel In Serial Out (PISO) shift registers, the data loaded onto register in parallel format. Whereas retrieved from it serially. PISO register which features a control-line and combinational circuit (AND and OR gates). Additionally to the essential register components (flip-flops) fed with clock and clear pins.