Hi Peter,
As far as I am aware the I2C interface in the 664 is indentical to that used in a variety of Philips controllers(552, 554, 652, etc). I can supply you with a well used assembler routine for single master. Drop me a mail if interested (email address is in my signature).

If it works partially I would look closely at the rise time on SCL and SDA. The risetime for 100kHz bus has to be better than 1us. Depending on your bus capacitance 10k may be a little high - we typically use 2k2 to 4k7.

Regards,
Graham
support at acqura dot com