Hi,
Try to find tech.note uC001:Using ADuc812 I2c Interface from www.analog.com/microconverter - i hope it is there - if not ,download full (free) package microconverter quick start development ,and in section "code" there are some asm routines showing how to use I2c - i2cadd and i2cdat are used in slave mode.Hope this will help.
Regards,Ioan Petrescu