TCA7408 is an 8-bit I/O expander for the two-line bidirectional bus (I2C) and is designed to provide general-purpose remote I/O expansion through the I2C interface.
The major benefit of this device is its wide VCC range. It can operate from 1.65 V to 3.6 V on the GPIO-port side and 1.65 V to 5.5 V on the SDA/SCL side. This allows the TCA7408 to interface with next-generation microprocessors and microcontrollers on the SDA/SCL side, where supply levels are dropping down to conserve power.
The bidirectional voltage-level translation in the TCA7408 is provided through VCCI. VCCI should be connected to the VCC of the external SCL/SDA lines. The voltage level on the GPIO-port of the TCA7408 is determined by VCCP.
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 direction bits. The data for each input or output is kept in the corresponding Input or Output register. All registers can be read by the system master.
TCA7408 has open-drain interrupt (INT) output pin that goes LOW when the input state of a GPIO-port changes from the input-state default register value. The device also has an interrupt masking feature by which the user can mask the interrupt from an individual GPIO-port.
