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SN65HVD1476DR Transmit Line Issue

Pavan Panchamukhi
Intellectual 260 points
Other Parts Discussed in Thread: SN65HVD1476

Hi

I am finding a typical issue in the SN65HVD1476 IC. I am able to receive the data on Rx+ and Rx- line. 

But same time, during transmission the data send is not observed on Tx+ and Tx- line. 

  • 0
    TI__Guru* 98535 points

    Hello Pavan,

    Do you have termination implemented between pins 9 and 10? If so what value? Also is the "Back 485 DE" signal logic high when you try to send data?

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Intellectual 260 points
    No i have not used any termination resistor.
    I am looping back the signals by connecting Tx+ to Rx- and Tx- to Rx+ , and am sending 0X01 on transmit pin.
    During the transmission am observing 0x7F on Receive pin.

    Also, tried Connecting Tx+ to Rx+ and Tx- to Rx- am observing no signals on Receive pin when 0X01 is send on Transmit line.
  • 0 in reply to Pavan Panchamukhi
    TI__Guru* 98535 points

    Hello Pavan,

    First of all the Tx+ and Tx- pins are labeled backwards on your schematic.

    Pin 9 = Y = Tx+ 

    Pin 10 = Z = Tx-

    So when you connected them backwards that is probably why you were able to receive data. As for the actual data you received, it is unclear what is going on in your data link layer, however you are saying that you are sending 0x01 = 1 base 10 and receiving 0x7F = 127 base 10. Is it possible that there is some sort of roll-over happening from the use of signed binary number format?

    My thought is that it doesn't seem coincidental that 0x7F = 01111111 in signed binary format and you are sending 0x01 = 00000001

    This is just a thought, but in any case, without knowing details of the communications protocol you are using it is hard to give any advice on the issue. 

    Best Regards,

    Casey