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BQ79600EVM: 2 BQ79600 interconected through COMH

Guillermo Oviedo
Prodigy 20 points
Part Number: BQ79600EVM

Tool/software:

Hello,

 

I’m currently using a pair of BQ79000-EVM boards to access the BQ7900 transceivers, and use them in the following scenario:

  • First BQ79000 translates from UART to daisy chain
  • Second BQ79000 translates from daisy chain to UART

 

Both BQ79000 are interconnected through daisy chain (COMH), and on the other side of each transceiver I have UART interfaces sending and receiving data.

I’m sending the wake up pings directly from my UART interfaces.

The following diagram should describe my current setup:

 

I’m currently able to send command frames of data from one UART interface to the other, but when I try to send reply frames, I can’t get the data on the other side.

 

I have the following questions:

  • Why I can’t sent reply frames in this setup?
  • Is the BQ79000 filtering reply frames?
    • If so, can this feature get disabled?
  • Can the BQ79000 be used just as a transceiver, and bypass all information from UART to Daisy chain?
    • Could the DEBUG_COMM_CTRL register be configured to follow this approach?
    • If not, is there a transceiver that could be purchased just for this purpose?

 

Thank you.

  • 0
    Prodigy 20 points

    Sorry I made a typo, with BQ79000 I was refering to the BQ79600.

  • 0
    TI__Expert 8705 points

    Hi, 

    This is a novel application scenario, nobody ever used it. We have no experience either. When the other MCU replies a response frame to 600's UART, 600 UART expects a command frame from MCU but it receives a response frame, 600 treats it as a byte error, according to the content below on page 16 of datasheet, 

    Bytes received on COMH/COML are NOT propagated up to the stack; while bytes received on the SPI/UART
    are propagated to COMH or COML depending on [DIR_SEL].
    • Even if there is a byte error, data is still forwarded from VIF to SPI (buffer)/UART; if there is a byte error, data
    doesn’t forward from SPI/UART to VIF.

    The debug registers don't help.

    If you only need very low speed communication, you can do like this: write something to one R/W register of one of the 600, the the opposite MCU reads this register. If you need 1Mbps communication, this way doesn't work. 

  • 0 in reply to Wayne Liu
    Prodigy 20 points

    Hello , thanks for your reply.

    Do you know if there is another transceiver that could be used for this prupose? Or if there is a way to disable this byte error detections in the BQ796000?
    Thanks.

  • 0 in reply to Guillermo Oviedo
    TI__Expert 8705 points

    Hello, no other way.