PCAL6534 34-bit General Purpose I/O Expander NXP Semiconductors PCAL6534 34-bit General Purpose I/O (GPIO) Expander provides remote I/O expansion for most microcontroller families via the Fast-mode Plus (Fm+) I2C-bus interface. The PCAL6534 fully meets the Fm+ I2C-bus specification at speeds to 1MHz. This device also implements Agile I/O, which is an additional feature set specifically designed to enhance I/O interface. These additional features include programmable output drive strength, latchable inputs, programmable pull-up/pull-down resistors, maskable interrupt, interrupt status register, and programmable open-drain or push-pull outputs. The ultra-low-voltage interface of the PCAL6534 allows for direct connection to microcontrollers operating down to 0.8V.