The FM3540/60 multiplexes the I-port input signals with two internal non-volatile registers that can be loaded through the serial port. The multiplexer is selected via the serial port and defaults to the I-Port upon power-up. Pull-up resistors are provided on the input port to accommodate connections to open drain outputs and to eliminate the need for external resistors. The device supports a choice of either 2.5V output or Open Drain Outputs for easy interface to devices with different VDD Levels.