DHOUSTON

Thanks for you comments.

1. The normal I2C clock is the SCL pin - and I agree it is driven by the PIC MCU. The 32768 Hz is needed by the MCLK pin and does something for the A to D process.

2. The question of the 5 volt tolerance of the chip - after a day of digging round on the web - seems to agree with your view. Philips has a good application note on bi-directional level shifting for the I2C bus (AN97055). I'll give it a go using 2N7000 MOSFETs

Regards Bill Legge