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Original question:

SN65HVD1782: J1708 Driver circuit

SN65HVD1781: RS485 and J1708 interface

Ganesh
Prodigy 20 points
Part Number: SN65HVD1781
Other Parts Discussed in Thread: TMUX1237, TMUX1119, TMUX1219

Hello,

I have to use common hardware circuit with SN65HVD1781 transceiver for both J1708 and RS485 interface with software change if required. I can make two assembly variant with minor component change, but not with transceiver part number change. There is a possibility of inversing the signal of UART Tx for DE in case of J1708 application. But my worry is Tx should be connected to D for RS485 and inversed Tx should be connected to DE, D should be grounded in J1708. How can I implement this two options in common circuit?

Please support

Regards,

Ganesh

  • TI__Mastermind 25705 points

    Ganesh,

    I think you could add external pull down resistor at D and REB pin. The setup is the same for REB pin for both applications. For TX, you either need two UART for D and DE, or use a 1-to-2 mux (TMUX1237) to route the input (one UART and one GPIO).

    Regards,

    Hao

  • in reply to Hao L
    Prodigy 20 points

    Hello Hao,

    Thanks for your suggestion. Is my below proposal works for both J1708 and RS485? Can you please provide your feedback? Will TI TMUX119 and TMUX1237  work with baud rate of 1.2k to 115.2k ?

  • in reply to Ganesh
    TI__Mastermind 25705 points

    The schematic looks good to me. I think either TMUX1119 (250MHz bandwidth) or TMUX1237 (400MHz bandwidth) should work. I also notify the TMUX expert in TI for further comments. 

  • in reply to Hao L
    TI__Intellectual 2694 points

    Hi Ganesh,

    For a 1ch, 2:1 SPDT switch requirement, you can use the TMUX1219 device and it will also help you with bom cost saving.

    The device supports a supply operation of 1.08V to 5.5V. The signal voltage supported on the channels is rail to rail i.e. 0V to VDD. 

    Also, the bandwidth of this device is high and more than enough to support the required baud rate.

    Just for your information, our precision series device TMUX1119 also works but will not be required for this use case.

    Thank you,


    Regards,
    Sandesh

  • in reply to Sandesh Rawool
    Prodigy 20 points

    Hello Sandesh and Hao,

    I will use TMUX1219 for my circuit. 

    Thank you both.

    Regards,

    Ganesha