The functionality of the ROM in the DS80C400 microcontroller can be accessed from programs written in 8051 assembly, C, or Java. By using this ROM and software libraries developed by the Dallas Semiconductor, many applications can be built. This application note describes how to start using the 8051 IAR Embedded Workbench to build applications for the DS80C400 in C. The DS80C400’s ROM functionality is demonstrated by implementing a simple HTTP server.