TCA9554A

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SCPS196D – DECEMBER 2010 – REVISED AUGUST 2015

8 Detailed Description

8.1 Overview

The TCA9554A open-drain interrupt (INT) output is activated when any input state differs from its

corresponding Input Port register state and is used to indicate to the system master that an input state has

changed. The INT pin can be connected to the interrupt input of a micro-controller. By sending an interrupt

signal on this line, the remote I/O can inform the micro-controller if there is incoming data on its ports without

having to communicate via the I2C bus. Thus, the TCA9554A can remain a simple slave device. The device

outputs (latched) have high-current drive capability for directly driving LEDs.

The system master can reset the TCA9554A in the event of a timeout or other improper operation by cycling

the power supply and causing a power-on reset (POR). A reset puts the registers in their default state and

The TCA9554A consists of one 8-bit Configuration (input or output selection), Input Port, Output Port, and

Polarity Inversion (active high or active low) registers. At power on, the I/Os are configured as inputs.

However, the system master can enable the I/Os as either inputs or outputs by writing to the I/O

configuration bits. The data for each input or output is kept in the corresponding Input Port or Output Port

register. The polarity of the Input Port register can be inverted with the Polarity Inversion register. All

registers can be read by the system master.

The TCA9554A is identical to the TCA9534A except for the addition of the internal I/O pull-up resistors,

which keeps P-ports from floating when configured as inputs.

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