• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 32 subscribers
  • Views 501 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

SN65HVD1471: Can the SN65HVD1471 device be used for RS-422 interface?

SN65HVD1471: Can the SN65HVD1471 device be used for RS-422 interface?

user4764564
Intellectual 380 points
Part Number: SN65HVD1471

Hi,

 SN65HVD1471 transceiver IC produces irrelevant output. To check hardware i just shorted Tx and Rx pins of IC and connected the differential pair by connecting 120 ohms across A,B and Y,Z, and given 3.3V to vcc pin and connected Gnd, Differential pairs are connected to PC via rs232 to rs422 convertor. But i haven't receive what i transmit for eg. if i send '1' i got 'g' as output. Could be please point out the mistake.

  • 0
    TI__Guru 62920 points

    Hello,

    Is this the way you have everything connected?

    1. PC serial port output -> RS-232 input of RS-232-to-RS-422-converter
    2. Corresponding RS-422 differential output of converter -> A/B differential input of HVD1471 (120 Ohms installed between A and B)
    3. R output of HVD1471 -> D input of HVD1781 (DE pin pulled to VCC, /RE pin pulled to GND)
    4. Y/Z differential output of HVD1781 (120 Ohms installed between Y and Z) -> RS-422 differential input of RS-232-to-RS-422 converter
    5. Corresponding RS-232 output of converter -> serial port of PC

    If so, I would expect you to receive the same character that was sent.  If not, can you please provide a diagram of the connections?

    Is it possible for you to loop back the RS-422 output of the converter back on itself so that HVD1781 is not in the circuit?  If the problem is still there, it may be in the converter or in the UART configuration of the serial port.  If the issue disappears, then it must be related to the HVD1781 connection.  In that case, you should probe the signal waveforms at each step described above to see at what point the data pattern changes.

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    TI__Guru 62920 points
    Also, it is important to make sure you have the right polarity on the differential signals and the wires are not reversed. Tables 3 and 4 in the datasheet give the logic for how high (1) and low (0) bits are represented on the differential interfaces. I mention this because the ASCII code for 1 is 0110001 and the ASCII code for g is 1100111. If the polarity were inverted and the bits were shifted by one position (e.g., due to a mis-interpreted "start" bit), then it would explain the behavior you are seeing.

    Max