TMS320F28335: I2C communication b/w two MCUs

Marada Naveen Kumar

Part Number: TMS320F28335
Other Parts Discussed in Thread: P82B96

I am trying to implement I2C communication b/w two boards containing F28335 MCUs in Master-slave mode.Every thing works fine when both are powered up.

whenever the slave is powered down,the Master is sensing bus busy and the voltage levels on the bus is changing from 3.3(Vcc) to 1.5V. I believe the issue is due to the common supply & ground and pull ups on the slave side are changing the voltage levels.when the slave is again powered up,i need to reset the I2C module through the software in Master for comm to happen. I've tried to eliminate this by placing diodes in the pull up paths at slave end,but still the issue repeats. Please suggest how to eliminate this ,Is there any alternative or other circuit config to communicate b/w two boards.The slave is supposed to be powered by the same supply of master,but can be powered off independently.

Thanks in advance,

Naveen M.

over 8 years ago

0 Adam Haun over 8 years ago

TI__Expert 8950 points

Naveen,

I2C is not designed for this. Putting the pull-ups only on the slave side should help keep the bus voltage at 0V during power-down, but the master will still need to be reset.

0 Marada Naveen Kumar over 8 years ago in reply to Adam Haun

Intellectual 615 points

Hi Adam,
If i keep the pull ups only on the Master side,will it eliminate this problem assuming that the master will never be powered down.Does the use of I2C Bus Buffers such as P8296B will help?

Regards,
Naveen M

0 Adam Haun over 8 years ago in reply to Marada Naveen Kumar

TI__Expert 8950 points

Naveen,

My thought was that if the pull-ups are the slave side, the slave SDA and SCL pins won't be pulled high when the slave is powered down.

I'm not sure if the P82B96 would help. You could ask on the I2C forum:

e2e.ti.com/.../390

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TMS320F28335: I2C communication b/w two MCUs