18F2480 I2C problem

[andrewg]

Well, I've solved it! Sort of.

I tracked the problem down to the line in the slave ISR "incoming = i2c_read();". It was getting stuck in there. Checking the assembly listing revealed just three instructions; it was checking the SSPSTAT "buffer full" flag and waiting until it got set before processing the data in the buffer. The flags must have been clear, but surely it should have been set (otherwise the interrupt wouldn't have been generated)? I couldn't find any code that clears that flag.

The fix was to replace that line with "incoming = *0xFC9;", i.e. ignore the buffer full flag and just read the buffer anyway.

I've checked the code for my previous I2C project (16F88 master and 18F4580 slave) and the code looks the same! Makes me very nervous that what looks like identical code should work in one place and not another!
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Andrew

[mpfj]

[andrewg]

You're right! Thanks, that looks much better.

I think ex_slave.c could do with an overhaul...
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Andrew