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SN74HCS596-Q1

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SCLS805 – JUNE 2020

Product Folder Links: SN74HCS596-Q1

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Copyright © 2020, Texas Instruments Incorporated

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

In this application, the SN74HCS596-Q1 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 SN74HCS596-Q1 does not need a

communication interface for control. It can be easily operated with simple GPIO pins.

The OE pin is used to easily disable the outputs when the displays need to be turned off or connected to a PWM

signal to control brightness. However, this pin can be tied low and the outputs of the SN74HCS596-Q1 can be

controlled accordingly to turn off all the segments reducing the I/O needed to three. There is no practical

limitation to how many SN74HCS596-Q1 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. Since the QH’

prime is push-pull, there is no need for a pull-up to drive High. 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,

the shift register needs to be cleared and then clocked into the output register. An RC can be connected to the

SRCLR pin as shown in Figure 12 to initialize the shift register to all zeros. With the OE pin pulled up with a

resistor, this process can be performed while the outputs are in a high impedance state eliminating any

erroneous data causing issues with the displays.