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Forum Index : Microcontroller and PC projects : I2C and pin 2

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Frank N. Furter
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Joined: 28/05/2012
Location: Germany
Posts: 831
Posted: 10:53pm 05 Mar 2014
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Hi,

I have the µMite beta 8 running on a 28 pin PIC32MX150F128 with a LED on pin 2.
When I activate pin 2 the LED lights up, but when I write something to IIC the light goes out???
Is there a relationship between IIC and pin 2 ???

Edit:
The same program works on 44 pin version correct... - LED doesn't go out...


FrankEdited by Frank N. Furter 2014-03-07
 
MOBI
Guru

Joined: 02/12/2012
Location: Australia
Posts: 819
Posted: 11:17pm 05 Mar 2014
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  Quote  Is there a relationship between IIC and pin 2 ???


There was an issue with pin2 in the first beta release as I recall. I wonder has it reappeared in a different form? Geoff?


=================
I just hooked up a LED to pin 2 and fired off i2c commands and light stays on with a zero out of pin 2 (sink mode) and gives a quick blink when pin 2 in source mode.

I'm using a 250F chip.Edited by MOBI 2014-03-07
David M.
 
Geoffg

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Joined: 06/06/2011
Location: Australia
Posts: 3196
Posted: 03:10am 06 Mar 2014
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This must take the record for the strangest bug ever.
I will investigate immediately.

Geoff
Geoff Graham - http://geoffg.net
 
MOBI
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Joined: 02/12/2012
Location: Australia
Posts: 819
Posted: 12:12pm 06 Mar 2014
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  geoff said  This must take the record for the strangest bug ever.
I will investigate immediately


It appears to do the same on pin 3 as well. Similar to the earlier beta. Pins 4,5,etc work ok.

A weird one?
David M.
 
Geoffg

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Joined: 06/06/2011
Location: Australia
Posts: 3196
Posted: 05:23pm 06 Mar 2014
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Yes, this one is weird and thanks very much to Frank and David for finding/confirming it.

The fault was caused by a bug in the PIC32 itself. Like every good programmer I had read the errata which said:
  Quote  Output High Voltage (VOH) on the RA0 and RA1 pins is not within the published data sheet specification if the I2C1 module is enabled.

OK, I thought, a few millivolts here and there will not make much difference.

But what they should have said was:
  Quote  Pins RA0 and RA1 will be totally stuffed if the I2C1 module is enabled.

(I can hear vasi reaching for the keyboard already).

The workaround is to disable slew rate control on the I2C pins. This was a "nice to have" thing but I don't think that it is critical. So I have disabled it in beta 9 which is out now.

I have tested beta 9 on my small collection of I2C devices and disabling slew rate control has not made any difference. But I would be grateful if as many people as possible could check their collection of I2C devices to see if disabling the slew rate has broken anything.

Thanks for everyone's help,
Geoff


Geoff Graham - http://geoffg.net
 
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