Hello Rainer
RPo wrote:

Hi,

I'm currently using the MPC5200 based board "PM520" and 
want to access the I2C bus. To do so, I attached a PCF8574P
to the bus. But I was not successful in setting the outputs
of this IC. 

<...snip..>

Revision of MPC5200? (third string engraved on the MPC)
If L25R then check this doco:
   http://www.freescale.com/files/32bit/doc/errata/MPC5200E.pdf
(if be short - I2C didn't work on this revision chips)

--
Regards
Andrey Volkov