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CC2538: CC2538 Custom Board I2C problem

Kanchan Debnath
Prodigy 250 points
Part Number: CC2538
Other Parts Discussed in Thread: HDC1080

Hi TI  Expert Team

I am working on TI  CC2538 based 6LoWPAN project,  I designed a number of custom board based on CC2538,  I have 2  I2C devices on the board ( an EEPROM and HDC1080) , in my earlier boards the I2C  used to work fine  for read / write both the EEPROM and HDC 1080 without any issue, however in my latest custom board, I2C bus is giving trouble.

There is only a minor change in the bus layout. The I2C bus lines both SDA and SCL are high and i see no transactions when both of the devices are connected ( EEPROM 24C04 and HDC 1080)
.

However if I take out the  HDC1080, the  EEPROM read write  works  fine.. my oscilloscope do not have a a i2c bus analyzer and its becoming  real difficult to find out the issues. It would be  great if you  can help me out. I can share all information( board layout , code etc )  if required.

Regards

Kanchan

  • 0
    TI__Guru** 106705 points
    Hi Kanchan,

    Is this a single board that fails? Are you sure the HDC1080 is ok? It sounds like it is pulling the lines high somehow.

    Cheers,
    Fredrik
  • 0 in reply to Fredrik K
    Prodigy 250 points
    Hi Fredrik,

    Thank you for your response. I made 10 board and of this i mounted the HDC1080 on 3 boards and all the three boards are behaving the same.
    If I take out the HDC 1080 it works fine, and when the HDC is not there if I check the bus lines on the HDC pads I can see the transaction.

    There is not much change in layout of the new and old board, the distance between the HDC and eeprom and HDC in earlier boards were around 3mm but in the new board its around 6mm.. Can this be a problem.. How long can the i2C bus works works fine?


    I need help to resolve this as I have an exhibition and need to showcase the product. Look forward for your support . All the HDC are new pieces that i got as free samples a few month back.. is it possible that if the IC HDC if not kept is air seal package can misbehave?

    Regards
    kanchan
  • 0 in reply to Kanchan Debnath
    TI__Guru** 106705 points
    Hi Kanchan,

    What values are you using on the pull-ups?

    Cheers,
    Fredrik
  • 0 in reply to Fredrik K
    Prodigy 250 points
    Hi Fredrik,
    I have used 10k pull up resistors... I have checked the pulse shape, it looks ok.. the pulses are slightly tapered at the top side , may be because of the rc time constant.. I will reduce the pull to 4.7K and check the pulse now and send you the snap shot. Do you think the 10 K value could be a problem..



    regards
    Kanchan
  • 0 in reply to Kanchan Debnath
    Guru 735685 points
    10K pull up resistor should be fine. If you disconnect EEPROM and keep HDC1080, does I2C work?
  • 0 in reply to YiKai Chen
    Prodigy 250 points
    Hi Sorry for the Late response , If I take ou one of the I2C Device it works. So both the EEPROM and the HDC1080 works but only one at a time. I am not really able to see any issues in layout that can affect the communication to such extent. All my earlier board works fine with the same board. Here in this case the bus line is simply high when both the devices are connected..

    Regards
    Kanchan