In this application, the SN74HCS164-Q1 is used to control seven-segment displays. Unlike other I/O expanders, the SN74HCS164-Q1 does not need a communication interface for control. It can be easily operated with simple GPIO pins. Additional control is provided with two serial inputs that feed into an AND gate.

At power-up, the initial state of the shift registers is unknown. To give them a defined state, the shift register needs to be cleared. An RC can be connected to the CLR pin as shown in Typical Application Block Diagram to initialize the shift register to all zeros.