John,

The I2C spec has suggested circuits for mixed voltage systems.

The spec is on Philips web site, I have it but lost the URL.
www.philips.com?

Also, if you are a 5 V master with 3 V slaves, you might be able to
just run the bus at 3V.  You'll need an 74LVCsomething to let your 5
V PICs drive the 3V SCL.  And you'll need to check the input high
voltage spec to see if a 3 V pull up is always a "1" when the PIC
reads SDA.  I did this to talk from 5 V PIC to 3.3 V MultiMedia Card
in I2C mode.

-Barry.
------------
Barry King, KA1NLH
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
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