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I2C errors with four-board MSP432 launchpad stack

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Hi, when I went from a two-board msp432 launchpad and SENSHUB stack to a four board stack, I started getting firmware I2C errors accessing the SENSHUB MPU-9150 IMU (on UCB0), but not the other sensors on the SENSHUB (also on UCB0).


The errors go away if I connect a protocol analyzer or scope probes to UCB0 I2C (via J2 pins on the SDCardReader). I have attached a scope screenshot of MPU-9150 initialization (which is working with the scope probe attached). 


Any suggestions for what to look for and/or solutions would be sincerely appreciated. The scope probe is a 10:1, with 10 MOhm & 17pF input, and the board stack consists of:




+-- SDCardReader BoosterPack (jumpered to UCB2 instead of default UCB0)


+-- MSP-EXP432P401R LaunchPad


\-- Protoboard (has UCB1 connector only for external I2C sensor)


Thanks for any help,



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Are there multiple boards with the I2C pull-ups installed? Too many pull-ups in parallel could lead to errors.

Alternatively, Having no boards with Pull-ups installed on the I2C lines means it should probably never work.

Also, If this is a signal integrity issue, you could try slowing the I2C clock rate down and see if the problem goes away.

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@@USWaterRockets, thanks for tip about slowing the I2C clock, I'll keep that in mind after investigating some firmware curiosities I noticed looking at all the I2C bus interactions. The SENSHUB boosterpack was and still is the only board on UCB0, and the I2C pull-ups are on the SENSHUB. All I've effectively done (AFAIK) is to add two more boards to the boosterpack bus (J1~J4), and one of the new boards now sits in-between the msp432 launchpad and the SENSHUB boosterpack (originally, the SENSHUB was the only board on the launchpad).

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