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Original question:

THVD4411: review the schmatic

THVD4411: Review the schematic

Aziz Gezer
Prodigy 20 points
Part Number: THVD4411

Tool/software:

Hi there,

I want to (have to) operate the THVD4411 with only 3 GPIO pins of our microcontroller. Shoul it work like in the following schematics?

  • GPIO-1 is assigned to DIR
  • GPIO-2 to Mode-0
  • GPIO-3 to Mode-1, TERM_TX and TERM_RX
  • SHDN = always VIO (Device always enabled)

I want to use the Mode-1 signal for terminal resistors as well since this signal must always high if any RS485 mode is chosen.

  1. Do you see any problem if the terminal resistor on the R3/R4 is also enabled on the RS485 half duplex mode?
  2. SHDN = always VIO (Device always enabled). Should it be OK if the device is always enabled on the RS232 mode.
  3. Are the function names OK on the common connector X13?

Thank you very much!

Best regards,

Aziz

  • +1
    TI__Guru 73221 points

    Hi Aziz,

    Aziz Gezer said:
    Do you see any problem if the terminal resistor on the R3/R4 is also enabled on the RS485 half duplex mode?

    The R3/R4 resistor is disabled when the device is configured to be in half duplex mode so you shouldn't run into any problems with this.

    Aziz Gezer said:
    SHDN = always VIO (Device always enabled). Should it be OK if the device is always enabled on the RS232 mode.

    Yeah, holding SHDN high is okay. SHDN is basically just for power savings.

    Aziz Gezer said:
    Are the function names OK on the common connector X13?

    Is X13 a DB9 connector? Or is this a standard 2x5 header connection?

    Aziz Gezer said:
    I want to (have to) operate the THVD4411 with only 3 GPIO pins of our microcontroller. Shoul it work like in the following schematics?

    One comment I have is if you plan on toggling DIR in half duplex mode for RS485, consider adding a pull up resistor on L1. (Can be something like 20k) When DIR is high the L1 output becomes high-Z and can float. This can cause glitches to the MCU/processor if it floats to GND. Having a pull up resistor on this pin would ensure a known state (you could also tie is low if you want the known state to be low, normally its high because most setups use UART and don't like break conditions from RX being low).

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points
    BOBBY said:
    Is X13 a DB9 connector? Or is this a standard 2x5 header connection?

    This is a 2x5 header connection. We use this board in different end products. So depending on the device there is either DB9 connector for RS232 or M12 connector on the device which are connected to the 2x5 header connector by a self-assembled cable.

    Thank you so much for your important comments.

    Kind regards,

    Aziz