The PCA9544A is a 4-channel, bidirectional translating multiplexer controlled via the I2C bus. The SCL/SDA upstream pair fans out to four downstream pairs, or channels. One SCL/SDA pair can be selected at a time, and this is determined by the contents of the programmable control register. Four interrupt inputs (INT3–INT0), one for each of the downstream pairs, are provided. One interrupt output (INT) acts as an AND of the four interrupt inputs.
A power-on reset function puts the registers in their default state and initializes the I2C state machine, with no channel selected.
The pass gates of the switches are constructed such that the VCC pin can be used to limit the maximum high voltage, which will be passed by the PCA9544A. This allows the use of different bus voltages on each pair, so that 1.8-V, 2.5-V, or 3.3-V parts can communicate with 5-V parts, without any additional protection. External pull-up resistors pull the bus up to the desired voltage level for each channel. All I/O pins are 5-V tolerant.