The TCA9535 is a 24-pin device that provides 16 bits of general purpose parallel input and output (I/O) expansion for the two-line bidirectional I2C bus or (SMBus) protocol. The device can operate with a power supply voltage ranging from 1.65 V to 5.5 V.
The TCA9535 consists of two 8-bit Configuration (input or output selection), Input Port, Output Port, and Polarity Inversion (active-high or active-low operation) registers. At power on, the I/Os are configured as inputs. The system master can enable the I/Os as either inputs or outputs by writing to the I/O configuration bits.
The TCA9535 is identical to the TCA9555, except that the TCA9535 does not include the internal I/O pull-up resistor, which requires pull-ups and pull-downs on unused I/O pins when configured as an input and undriven.