Why I2C Bus is busy with two devices?

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Anonymous
Not applicable

Good evening,

i'm trying to getting two MPU-9250 working via I2C with PSOC as Master.

Connecting to the bus only one MPU-9250 everything works perfectly!

Using two devices won't work, and the I2C_SendStart() says: I2C Bus Busy!

Testing without any device connected the I2C_SendStart() function says at first attempt: I2C_NAK (it seems the right answer when no devices answers to the call of the PSOC), after from the second attempt I2C answers Bus Busy!  To free the bus i have to use the I2C_SendStop() function, but i using it yet... but doesn't free the bus.

The MPU-9250 used is on a IMU breakout board by sparkfun: SparkFun IMU Breakout - MPU-9250 - SEN-13762 - SparkFun Electronics

Thank you for support!

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3 Replies
Bob_Marlowe
Level 10
Level 10
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Could it be that the pull up resistors from two devices are out of limit? Are you using a Cypress prototyping kit which also has gutpullups?

Bob

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Anonymous
Not applicable

I don’t know for sure..

Reading an NXT I2C datasheet i have read that for 400kbit speed i need a 1K pullup, according the IMU schema, it has an integrated 10K pullup.

So is possibile that one IMU works and 2 doesn’t for this reason?

Anyway i'm using a CY8KIT-059 (PSOC 5LP) Prototyping Kit

Il giorno 15 gen 2018, alle ore 21:43, user_1377889 <community-manager@cypress.com> ha scritto:

CYPRESS DEVELOPER COMMUNITY

Why I2C Bus is busy with two devices?

reply from user_1377889 in PSoC 5 - View the full discussion

Could it be that the pull up resistors from two devices are out of limit? Are you using a Cypress prototyping kit which also has gutpullups?

Bob

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Hi,

You can check on the pull up resistor limits from Section 7 of https://www.nxp.com/docs/en/user-guide/UM10204.pdf (NXP I2C specification).

Thanks,

Shanmathi

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