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MAX3232E: Two Device RX232 TX lines are connected to gather and one device transmit data other device is IDLE what are implications?

Murali Krishna
Prodigy 95 points

Part Number: MAX3232E
Other Parts Discussed in Thread: MAX3222E, MAX3232

Hi Team,

Two devices have their RS-232 transmit (TX) outputs connected together. One device is actively transmitting, while the other is idle. What issues or risks could arise from this configuration?

if it is risk arise what are mitigation on HW change?
  • 0
    Guru 325980 points

    The RS-232 bus does no specify an idle state. If you connect the outputs of two MAX3232E drivers together, the data will be corrupted.

    You need a device like ther MAX3222E where you can disable the drivers with the /PWRDOWN pin.

  • 0
    Prodigy 95 points

    Two DUT devices have their RS-232 transmit (TX) lines tied together and interfaced through a MAX3232 on the daughter board. When one DUT is actively transmitting, can the data be received at the connector without issues? Additionally, what risks or contention problems could arise from connecting two RS-232 TX outputs together from DUT's?

    Please find the screen shot.

    if it is risk arise what are mitigation on HW change in Daughter board?

  • 0 in reply to Murali Krishna
    TI__Mastermind 28032 points

    Hi Murali,

    I echo Clemens' comment above. Having 2 TX lines connected together on the same line violates the RS-232 standard. We do not recommend doing this. You will likely need to use a MUX or designing it where only one TX line is connected at a time. 

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    Guru 325980 points

    And two receivers connected together also violates the RS-232 standard.

    You need two RS-232 transceivers (or one chip with more channels). Between the transceiver and the CPU, you can combine two RX lines with an AND gate.