Trouble shooting I2C

ferrumvir · Joined: 01 Feb 2006 Posts: 64 Location: England

I found a couple of stumbling blocks using I2C, hopefully this post will stop other people tripping on them like I did.

1/ Don't try the I2C without the pull up resistors (4.7k Ohms), this will effectively hang the PIC which will require the watchdog to recover. Don't ask my why, it just does.

2/ Don't use the routine "setup_spi(FALSE);" as this will also the I2C working. I had copied the setup used on several other projects and didn't realise that this would cause problems... But it did.

For those who'll ask, compiler v3.249, PIC18F2680 & PIC18F258.

Cheers Scott

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Reason why it hangs if you leave off the pull-ups:
http://www.ccsinfo.com/forum/viewtopic.php?t=30751&start=3

Reason why setup_spi(FALSE) disables hardware i2c:
http://www.ccsinfo.com/forum/viewtopic.php?t=29669&start=3

ferrumvir · Joined: 01 Feb 2006 Posts: 64 Location: England

Thanks for the info, I searched the forum before I discovered my errors and failed to find anything, I also searched before I posted, nothing.

This highlights my inability to know what keywords to search for!

Fingers crossed it'll help someone...

Cheers Scott