I'm not certain where your problem is coming from, but here
are my I2C notes about I2C devices:

1. I2C devices are simple state machines. But powerup does NOT place
the device in a known state. In fact, every I2C device on the bus might be
in a state that seizes the SDA bus. The easiest way to initialize is to 
execute
clocks until the SDA bus is released. The maximum number needed is 9 clocks.
If the SDA cannot be freed after 9 clocks, you either have another master
driving the bus, or you have a defective i2c device on the bus.

2. Synchronize the bus by performing a STOP flag, followed by a START
flag then a final STOP flag. At this point, all I2C devices on the bus are
initialized and will execute properly from then on.

3. I never use pullups lower than 3.3K on 5V buses, 2.2K on 3V buses.
SOME I2C devices can't pull down a heavier resistor.

4. After a master has finished with the I2C bus on a multi-master system, it
must release (tristate) both pins immediately. This is naturally easy to do,
because the STOP flag causes both pins to be in the '1' state anyway.

5. I have heard of i2c buses being run  over a meter distance, etc. This
is not a good idea, because line reflections become a problem . I2C is
a communication system designed to control TV components using few
wires, and it works fine as long as the bus stays on the same PCB.

--Bob



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