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Serial test error for RS422

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  • Serial test error for RS422

    Our motherboard product has 2 x RS232 ports and 2 x RS422 ports. We would use serial test item to verify their functions.
    RS232 port is a standard DB9, thus I can connect a loopback plug for testing its function by BurnInTest utility. The result is OK.

    RS422 port has 5 pins including TX+, TX-, RX+, RX- and GND. I think it's a differential signal.
    I wire TX+ to RX+ and TX- to RX- as a loopback situation. Then I can use Teraterm terminal to check TX and RX data loopback transmission. The result is OK.
    I select serial test item in BurnInTest in order to test this RS422 port
    In Serial ports configuration of BurnInTest, I select "Disable RTS/CTS and DSR/DTR test phase" in advanced.
    Press START to test RS422. The result is failed.
    I get a error message quickly. It is "Error while receiving from the COM port. Check plug is connected."

    Does BurnInTest support RS422 testing ?


  • #2
    If you have a RS422 to RS232 adapter and then use our serial loopback plug it should work.

    I think there more to making a working RS422 loopback than just joining TX to RX.


    • #3
      Hi David,
      I connect a RS422 to RS232 adapter and then use serial loopback as well.
      The result is still failed. The same error message on the screen.
      observe we only have RX and TX pin on RS422 interface. The loopback only is for RX and TX.
      Other CTS, RTS, DTR and DSR pins are empty function. Maybe this is the reason why I get the error message.

      I need to test serial data transmission between two COMs (Ex. COM1 to COM2)
      Does BurnInTest support this type of serial testing ?



      • #4
        If you only have two working pins on your RS422 connector, then it isn't really RS422. It's something else, a custom connector.

        I don't know how your custom system works, but on most systems it is required that CTS and DTR are pulled high before any transmission can take place.

        But this is a 45 year old standard now, that isn't used very much, so there aren't many people left in the industry who remember how it all should work.

        i.e. you might need to do some research and experimentation.