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MAX3232 - Connecting cable floating issue

Part Number: MAX3232

Dear E2E,

After RS232 transceiver, connect a long cable like 12M and then floating it. will it cause wrong detection issue?

Actually, it should connect to PC. When they disconnect it on PC side, but the cable still connect on system side and it looks like floating.

CPU is still doing the detection RS-232 port even the cable is disconnected on PC side so that CPU pending in this step.

Could you guide us the reason?

BR,

Jason 

  • Jason,

    Which pin the cable is connected to? Is a Dout (output) or Rin (input)?

    If the port is for handshaking, you can short it to PC output. You can refer to this page for the connection of "Null modem with loop back handshaking".

    www.lammertbies.nl/.../RS-232_null_modem.html

    Please let me know if you have more questions.

    Regards,

    Hao

  • Hi Hao

    about you question
    Which pin the cable is connected to? Is a Dout (output) or Rin (input)?
    we have use four signal TX,RX,CTS and RTS.

    for this case, this is the process of recurring problems ,
    1. our DUT(host) connect PC (slave) with 12m ethernet cable.
    2. power on , and it is work fine.
    3. power off , we remove PC (slave), but the 12m ethernet cable still connect DUT(host).
    4. power on, our DUT is waiting stage,it can not boot finish.
    5. remove ethernet cable, the DUT can continue boot.

    this problem is host connect long cable (no connect slave), is this violation RS232 rule ?

    Thanks
  • hello Hao,
    any comment on customer's question?

    BR,
    Jason
  • Jason,

    Thanks for your information. However I need to confirm a few more.

    Let's assume DOUT1 is TX, RIN1 is RX, DOUT2 is CTS, RIN2 is RTS.

    Are all four pins connected to PC with an individual 12M cable?

    When PC is disconnected, are all 4 cables still there?

    When the cables are removed, the DUT can boot again. Did you remove all 4 cables at once?

    I'm looking forward to your answer.

    Regards,

    Hao

  • Hao,

    Please see our reply for those question.

    Are all four pins connected to PC with an individual 12M cable?

    [Jason] it connect to RJ45 connector and then through ethernet cable connect to PC. so, not individual cable.

    When PC is disconnected, are all 4 cables still there?

    [Jason] yes, ethernet cable is still connected on DUT.

    When the cables are removed, the DUT can boot again. Did you remove all 4 cables at once?

    [Jason] DUT will not boot again, just pending for waiting something. once cable connect back again, the system can continue running.

    customer's question is that if connect cable on DUT, but floating on PC side. will it violate the RS232 standard?

    BR,

    Jason

  • Jason,
    I don't think leaving floating cables violates any RS232 standard. Theoretically it would only add some parasitic capacitors on the output pins. I think we need to find out what changes by taking this action. If you could, I suggest you start the debug by comparing the waveforms of the pins with and without the Ethernet cable.
    Regards,
    Hao
  • Hi Jason,

    Have you had a chance to look more into this based on Hao's suggestion?

    Regards,
    Max