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SN65HVD1781A-Q1: SN65HVD1781A-Q1

SHivaraju MB
Prodigy 40 points
Part Number: SN65HVD1781A-Q1

Tool/software:

I am using the IC "SN65HVD1781A-Q1" for converting the UART to RS422 signal using the microcontroller P/N. TMS320F28335ZJZQ.

as per data sheet, suppose to get the loopback signal from the pin 1 (R-Receive) of SN65HVD1781A-Q1. but not getting any out on Pin 1 when checking for loop back. but when RS422 signal provided to Pin A and B the UART signal is available in pin 1 of SN65HVD1781A-Q1.

Please provide, if any configuration changes or is there any solution for the issue. As per data sheet the following is the diagram. 

   

using this configuration to convert from UART to RS422.

  

  • 0
    TI__Guru 73971 points

    Hi Shivaaraju,

    You should definitely be able to see a loopback on the R pin if you're driving the D pin. The only thing I can think of why you wouldn't is if the driver is disabled, then the inputs on the D pin will not make it to the A/B pins and loop back into the R pin.

    Are you able to put an oscilliscope on the DE, D, and R pins? Also get a scopeshot of D, A, B, and math of (A-B)?

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 40 points

    No not getting the data on R pin. I have used the pin 2 to Ground and 3 tied to High.

    not getting the data on R pin. Is there any other configuration required?

  • 0 in reply to SHivaraju MB
    TI__Guru 73971 points

    Shivaaraju,

    Your configuration is correct. There is likely something wrong with the device or the PCB/system if you are not able to see the R being mirrored. 

    Can you verify the soldering is correct without any shorts? Does removing the device and adding a new one fix the issue?

    -Bobby