8 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, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

In this application, the SN74ACT596-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, one per LED, to only four. Unlike other I/O expanders, the SN74ACT596-Q1 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 SN74ACT596-Q1 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 SN74ACT596-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. 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.

SN74ACT596-Q1

SCASE34 – NOVEMBER 2024

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