This application note demonstrates how to write an Inter Integrated Circuit bus driver (I2C) for the XA-S3 16-bit Microcontroller from Philips Semiconductors. Not only the driver software is given. This note also contains a set of (example) interface routines and a small demo application program. All together it offers the user a quick start in writing a complete I2C system application with the PXAS3x. The driver routines support interrupt driven single master transfers. Furthermore, the routines are suitable for use in conjunction with real time operating systems.