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THVD1420: THVD1420 Shared USART and Pin Configuration

Michael Veenstra
Prodigy 20 points

Part Number: THVD1420
Other Parts Discussed in Thread: MAX3223, THVD4421

My system can be configured for RS232 or RS485. I'm wondering if it is possible to split a USART pin pair between THVD1420 and the MAX3223? I'm worried about leakage current and if the signal integrity will be okay. Either one or both converters may be powered (MAX3223 is dual channel so other RS232 channel may require converter to be powered), but only one will control TX. The user will communicate with either RS485 or RS232.

Alternativley, I have the THVD1420 & MAX32223 on separate USART pin pairs. When I don't want to use the THVD1402, I remove power from the converter but leave GND connected. What should I configure my MCU's USART pins in this situation? GPIO Output with pulldowns? 

  • 0
    Guru 324920 points

    UART signals are high when idle. Add pull-ups to the RX signals, and/or combine them with an AND gate.

  • 0
    TI__Guru 54042 points

    Hi Michael,

    Clemens is correct if you are going to do your multi-protocol application discretely. There could be potential contention issues depending on power state of the devices and you could cause issues with what you are looking to do. 

    That being said - you may also want to look at the THVD4421 - it is a 2x2 RS-232 transceiver combined with an RS-485 transceiver - you can only use one bus at a time would be the downside - but from a protocol level it may fit in your system better. 

    Best,

    Parker Dodson