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I2C bad electrical ACK?

Question asked by flown.tesca on Apr 27, 2015
Latest reply on Apr 27, 2015 by flown.tesca

I try to use I2C between STM32F103 + ATMEGA32.

Side ATMEGA, my I2C program Master/Slave works at 300% sure in all mode.
Side STM32, that's the part I try to make work.

In first test, STM32 is in Master Transmit (at 25KHz) and ATMEGA is just slave receiver.

- STM32 send start -> ok
- STM32 send Address + Write -> ok ( ATMEGA goes well in slave receiver and ready to accept data )

But I have always ACK failure on STM32 side.

Look my screen scope of electrical measure:

We can see that the ATMEGA try to low the line but don't success to do it. That's my problem.

Pull-up is 2.2KOhms resistor, Like I said I'm sure ATMEGA works fine, I tested it with another IC. But as soon as I plug it to STM32, ATMEGA can't low the line to ACK.

That's my first shot with STM so if someone has an idea? I put PINB6 and PINB7 in alternate output function, is it right?