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I2C on devboard

PostPosted: Tue Feb 03, 2009 6:41 am
by dteney
Hello,

I'm trying to use the I2C bus on the Pumpkin CubeSat kit devboard. I have some code that reads the temperature from a LM75 sensor, and that works great on TI's(minimal) MSP430 board (the board with just the bare CPU). However, it doesn't work on Pumpkin's devboard; for some reason the MSP430 never receives data on the I2C lines.

Does anyone have an idea of what could be the small difference between the two boards that perturbs the I2C bus ? (the SD card reader ?? FYI I'm not using it)

Thanks in advance for your help,

Damien Teney

(Moved to CubeSat: Electrical)

[This message has been edited by aek (edited February 03, 2009).]


Re: I2C on devboard

PostPosted: Tue Feb 03, 2009 7:03 am
by aek
There is no I2C support on the CubeSat Kit architecture Revs A through C. Therefore, you have to facilitate a way for I2C to get from the MSP430 (P3.1 & P3.3) to SCL_SYS and SDA_SYS.

We issued a Memo (see customer download area) on this, and suggested a discrete circuit to do this. A better / easier way to this is to use e.g. a PCA9515A.

Rev D onwards has I2C "built in".

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Re: I2C on devboard

PostPosted: Tue Feb 03, 2009 7:09 am
by dteney
Hum, I didn't use the I2C pins of the CubeSat bus, but I used directly the P3.1 and P3.3 pins. Shouldn't it work then ?

I read the memo about I2C, but my understanding is that it was a concern only for users wishing to use both I2C and SPI devices on the MSP430's UART0.

[This message has been edited by dteney (edited February 03, 2009).]

[This message has been edited by dteney (edited February 03, 2009).]


Re: I2C on devboard

PostPosted: Tue Feb 03, 2009 7:18 am
by aek
Did you add pullups?

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Re: I2C on devboard

PostPosted: Tue Feb 03, 2009 7:32 am
by dteney
Yes I did, 2K2 resistors.

Re: I2C on devboard

PostPosted: Tue Feb 03, 2009 7:56 am
by aek
Sounds like you're doing it right. Make sure that nothing associated with the SD Card is active. Some customers have run I2C without SD card present, when driving direct on P3.1 and P3.3.

At this stage of debugging, I find that a 'scope" (to search for I2C waveforms) is what you need. Once I2C waveforms look good, then I switch to a Beagle USB analyzer from Total Phase.

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