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SN65HVD75: RS485 not working properly

Part Number: SN65HVD75

Hello Friends, 

recently, i've made an BLE to RS485 interface board. ( it contains nordic's BLE soc; Sorry for that )

anyway, i've done my artwork and order pcb and hand soldered the pcb.

but some boards only can Receive ( Transmit not working ) , And the others can only Transmit 

what's the problem ? did chip die when i do hand soldering ?  if i do SMT process is it work properly ?

i attach my schematic , i need your help freinds !

  • Hi Bongjin,

    thanks for reaching out! In order to do trouble shoot your RS-485 solution effectively - lets clarify some circumstances.

    1. Have you done a sanity check: Verify that Vcc and logic rails have proper voltage levels.
    2. How many nodes are connected to the RS-485 bus?
    3. Are the problems reproducible or do they occur random? 
    4. How many boards have you done and how many have this issues - do some of them work correctly? - do some not work at all?

    I can't see any faults on the schematic so far. Do to a statement if you had overheated the device during the soldering is difficult.

    A good thing to do is to measure the signals D, DE, R, RE connected to the SN65HVD75. Disconnect all nodes for this test. If possible, please share your wave-forms so we can make sure this is not the root causing the troubles.

    Kind regards 

    Dierk Bronner  



  • hello Bronner,
    Thank you for your Reply !
    i've solve the problem, i removed targert RS485's Pull-up and Pull-Down Resistor !

    i've got some tips that i have to check

    i really appreciate for your reply.
    Thank you very much and have a nice day :)
  • Hi Bongjin,

    that's good news, I'm glad to hear about your success. Thanks for the feedback and have a great day as well!

    Kind regards 

    Dierk