The I2C interface has become a popular way to hook up external devices to microprocessors. However popular the I2C bus may be, there are still many peripherals that use a parallel interface. This article presents a low-cost I2C port expander that can be used to control peripherals without an I2C interface. Our example shows how to connect the General Purpose Driver Interface to an alphanumeric LED display.I2C slave devices range from simple input/output ports to complex parts like EEPROMs. Devices without an I2C interface can be connected to the I2C bus by means of a Slave microprocessor with I2C hardware. This solution makes the slave ‘smarter’ and takes some load off the main processor but the disadvantages are that a Slave microprocessor adds cost to the system while software needs to be developed for both the Master and Slave processor. I2C port expanders are a good alternative to interface peripherals to the I2C bus.