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 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, one per LED, to only four. Unlike other I/O expanders, the SN74HCS596 does not need a

communication interface for control. It can be easily operated with simple GPIO pins. 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. All storage register outputs are open-drain.

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 can be

controlled accordingly to turn off all the outputs reducing the I/O needed to three.

There is no practical limitation to how many SN74HCS596 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. The QH' pin is a push-pull output, which does not require a pull-up resistor to operate. It is also

always active, regardless of the OE pin input state.

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 circuit can be connected

to the SRCLR pin as shown in the Typical Application Schematic below 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.

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SN74HCS596

SCLS840 – AUGUST 2020

Copyright © 2020 Texas Instruments Incorporated

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Product Folder Links: SN74HCS596