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I2C: How slow is too slow for a USCIB0 slave?

Ezekiel
Genius 3150 points

I have the unenviable task of talking to a really old RTU that is bit banging I2C at approximately 70hz. Yeah, it's old and slow.

I'm struggling with an unexpected I2C issue - the MSP430's I2C port can't run that slow.

I'm using a G2553 and I've assigned P1.6 and P1.7 to I2C duties.

I've configured the USCIB as a slave port.

I've then connected up the Master device to the MSP430.

When the old RTU talks to the MSP430, all the MSP430 does is set the USBBUSY flag occasionally.

What is the slowest speed that the USCIB port will talk as a slave device?

  • 0
    Genius 3150 points

    Well, I have a solution from the guys over at 43oh.com. I failed to read the documentation carefully.

    "Check out USCI I2C documentation, you have to shift device ID >>1, it takes only 7 low bits unlike what you see on the bus. That's the reason why your slave doesn't send ACK."

    My thanks and Kudos to V0JT4 in the Czech Republic!

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