> In setting up the I2C mode on a 16c73a for a slave, the TRISC bit for the
> SDA and SCL line are configure as input;
Correct assuming you are using the SSP hardware in slave mode.

> also the corresponding PORTC
> latches are cleared.
Not required but no harm done.


> However when I check with a scope, I found out that
> these open drain collector output a voltage (+5V) on the bus masking the
> signal from the master.
How can you tell with a scope who is driving what?  Are you sure the
PIC is driving the pins?

> I don't know what I am doing wrong but this seem
> weird.
> The master definitely works because I clearly can see the start condition on
> the scope.
If you can see the start condition, then SDA is not locked
high.  Is the Start still valid with the slaves on the bus or only if
you disconnect them?  If the slave is disconnected do you see a valid
command byte to the slave address that is Not Acked?

> What am I doing wrong? Should I post the code that I use to initialize the
> SSPCON?


> What are pull up resistors anyway?
Are you asking "what is a pull up resistor?".  If so, please refer to
the archives for a (very long) series of posts entitled "Arrg, this
is so confusing".

If you are asking "what value to use", this depends on speed of bus
and on bus capacitance.  Try 10 K Ohms for a short 100 kbps bus.  If
risetimes are too slow, try smaller values 1 K Ohm or so is a
practical minimum.  If bus low voltage is too high or if power
consumption is as issue, try larger values, I use 15K in one project
here with a short bus.

Hope this helps.

------------
Barry King, KA1NLH
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
Hinesburg, Vermont, USA
barry@nrgsystems.com
"The witty saying has been deleted due to limited EPROM space"