Hi Peter,

It took me awhile, but I was finally able to find some I2C documentation at Analog Devices website. They evidently aren't familiar with creating app notes with titles reflecting their contents. The ADuC812 datasheet doesn't mention I2C, just SPI. The 812's Quick Reference Guide does mention it, with sfr bit definitions, but nothing to indicate how it is used.

Anyway, I found (in spite of them) their tech note uC001 which describes the ADuC812 I2C interface. This is located at http://www.analog.com/library/a.../uC001.pdf

It turns out that their I2C master is software with a tiny bit of hardware support. I2C slave is supported by hardware (which makes sense, because I2C slave would be difficult to implement in software without a very fast uC).

Anyway, the tech note gives full example asm code for I2C master and slave, complete with flow chart for send and receive. You should be able to extract from it the I2C master functions you need to access your RTC chip. Your code has some delays in it that I don't think are necessary; the RTC chip should be able to take data at 100 KHz, if not 400 KHz. The example code (for 100 KHz) doesn't use any delays in the I2C interface.

Good luck!

Dennis