Integrated Circuit

HD74LS166A 8-bit Shift Register

The inputs are buffered to lower the drive requirements to one series 74 or 74LS standard load, respectively. Input clamping diodes minimize switching transients and simplify system design. This parallel in or serial-in, serial-out shift register has a complexity of 77 equivalent gates on a monolithic chip. This device features gated clock inputs and an overriding clear input.

The parallel-in or serial-in modes are established by the shift / load input.

When high, this input enables the serial data input and couples the eight flip-flops for serial shifting with each clock pulse. When low, the parallel (broadside) data inputs are enabled and synchronous loading occurs on the next clock pulse, during parallel loading, serial data flow is inhibited.

This, of course, allows the system clock to be free running and the register can be stopped on command with the other clock input. The clock-inhibit input should be changed to the high level only while the clock input is high. A buffered, direct clear input overrides all other inputs, including the clock, and sets all flip-flops to zero.