Paul:
You should look at the Analog Devices web site at www.analog.com. They have some pretty comprehensive support files for the various MicroConverter series parts. For example, the ADµC831 section of the site has a ZIP file full of sample code which you can download from...

831code_asm.zip

...the download file has code samples showing how to implement I²C protocol for both Master mode and slave mode.

Have at it.....
Michael Karas