Motion Sensor SPI / I2C minor issue

Andy Green andy at
Wed Jan 23 15:06:48 CET 2008

Hash: SHA1

Somebody in the thread at some point said:
> Andy Green wrote:
>> The chip supports I2C and SPI on the same pins, they use the SPI CS to
>> select I2C mode when it is disabled for SPI.
> Oh crap :-( Remove one ?

I guess we should go on and then analyze carefully what data we clock
out to poll.  I2C has this start and stop bit concept, it can be that
there is no possibility to hit the magic I2C address after any apparent
I2C "start" bit... then we're okay.

Hey another idea maybe if we strobe the other CS after every clock it
acts to continually reset the I2C state machine in the other device,
while not affecting the bus transaction with the enabled device.

If none of that will help... yeah remove one or route a different GPIO
to be the clock of one will fix it as well.  But its not so unlikely we
can get away with it I think.

- -Andy
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