Hi Marc,

there is only one I2C protocol.
And also 2 additional high speed modes are defined.
But every I2C device can communicate until
the standard speed maximum of 100kHz.

The 80C552 hardware I2C is very powerful with a lot of functions
especially for multi master applications.
But for the LM75 you need only single master transmit and receive.
Nevertheless you must implement all others to avoid hanging bus
states. And so the driver software must be very complicated.
Also to profit from the speed advantage of a hardware I2C
you must implement it as an interrupt handler.
See at the Philips application notes to get an impression
of its complexity.

So my suggestion, use a software I2C master, e.g.:

http://www.specs.de/~danni/appl/hard/i2c/index.htm

I use the Dallas DS1621 temperature sensor and can
you give software examples for it.
I think it must be similiar or can easy adapted
to the LM75 (compare the data sheets).


Peter