Tilmann:

The I²C peripheral on your processor works similar to the I²C/SMBus peripheral on a Cygnal C8051F126 controller. I used this peripheral in support of an AT24C01 serial EEPROM with interrupts and found the overall code size small. The code is shown in the the document linked below and contains well commented assembly language including the routines that support the EEPROM device specifically. Look in the attached listing from code label _EE_WRITE: through the end of the subroutine at label SMBus_MRDBNACK:. Looking at the assembler output listing I found this to use 248 bytes. (That does not include the interrupt vector itself)..

Loader code with I²C ISR Implementation

Michael Karas