JAJSM30A October 2020 – May 2021 SN74HCS594
PRODUCTION DATA
In this application, the SN74HCS594 is used to control seven-segment displays. Utilizing the serial output and combining a few of the input signals, this implementation reduces the number of I/O pins required to control the displays from sixteen to four. Unlike other I/O expanders, the SN74HCS594 does not need a communication interface for control. It can be easily operated with simple GPIO pins.
There is no practical limitation to how many SN74HCS594 devices can be cascaded. To add more, the serial output will need to be connected to the following serial input and the clocks will need to be connected accordingly. With separate control for the shift registers and output registers, the desired digit can be displayed while the data for the next digit is loaded into the shift register.
At power-up, the initial state of the shift registers and output registers are unknown. To give them a defined state, both registers need to be cleared. An RC can be connected to the SRCLR and RCLR pins as shown in the Typical application block diagram to initialize the shift and output registers to all zeros.