# Forum: ARM programming with GCC/GNU tools AT91SAM7A3 TWI controller

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I was wondering if anyone here had worked with the TWI on the 7A3 (and I
guess the 7S, since I think they are basically the same one).  I've been
having trouble with the clock hiccuping.  To save time, I'm going to
copy and paste what I posted on the AT91 forums, so if anyone reads
there, you'll have seen this before.  No one has responded to that one
though, so I thought I'd post it here.

I have it talking to an AVR mega644 chip, sending commands and getting
data rather reliably, but sometimes the clock hiccups. I have a logic
analyzer on the data and clock lines of the TWI, and it is running at
3k, making each low period 150 uS and each high period 150 uS.
Occasionally the TWI clock line is held down for 300 uS, and then pulled
up for 150 uS. This confuses the heck out of the AVR, and I get a bad
data transaction. Why can't the TWI controller keep a steady clock?

Anyone else seen a similar issue and figure out a way around it?

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