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TMS570LS3137-EP: I2C Rx Data register (I2CDRR) gets assigned garbage value upon read

Subash Sundaresan1
Intellectual 560 points
Part Number: TMS570LS3137-EP


We are using on chip i2c module for sensor interface and it is working fine. However upon read data from Rx data register (I2CDRR), the I2CDRR is gets assigned to 0x0080. There is no such information in TRM. Could you please explain this behavior?  

  • 0
    TI__Guru**** 198766 points

    Is 0x0080 not the new received data? Did you probe the I2C data bus to check if this data is sent from another I2C node?

  • 0 in reply to QJ Wang
    Intellectual 560 points

    Definitely 0x0080 is not the received data as we are reading data from temperature sensor. It looks garbage data. we haven't probed the i2c lines yet. When we are reading the data from I2CDRR when the "RXRDY" is set is correct data. However after reading data from I2CDRR , it gets 0x0080. At the next cycle we are receiving sensor data and the cycle goes on.

    When We are reading the data from I2CDRR by using a CCS command "this.debugSession.memory.readRegister(RegisterName)", through the Scripting Console, the read is successful, data is read, but RXRDY bit of I2CSTR is not cleared. Also, I2CDRR retains the data.

  • 0 in reply to Subash Sundaresan1
    TI__Guru**** 198766 points

    The RXRDY flag should be polled to determine when to read the received data in the I2CDRR. The RXRDY flag is only set when the received data in the shift register has been copied into the data register. 

    If the read is not from CPU or DMA, the RXRDY is not cleared.