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SN65176B: SN65176B connection problem

Michael Soldierram
Prodigy 40 points
Part Number: SN65176B
Other Parts Discussed in Thread: THVD1450, THVD1550

Tool/software:

Hello
We want to make a connection between the SN65176BDR product and the STM32F401RET6 MCU. We had some problems while drawing the SN65176BDR. Our drawing is below. What are its shortcomings? What do we need to add?

Thanks.
Michael

  • +1
    TI__Guru 72751 points

    Hi Michael,

    Michael Soldierram said:
    We had some problems while drawing the SN65176BDR.

    Do you have any additional details about this? Was there any testing done that showed some sort of issue when using the device?

    Only real problem I see is the 1k series resistors on D and R are going to affect the data rate. These resistors are fairly large, you may need to size them down to 50 ohms if you think you actually need them. Most causes you won't need series resistors, maybe just make them 0 ohms.

    This device is also doesn't have an internal fail safe feature so if you use it as a receiver and there is no active driver, the state of R is unknown. I would probably recommend placing a pull up resistor of ~700 ohms on A and a pull down resistor of ~700 ohms on B. 

    When DE/RE# is toggled, the R goes high Z if RE# is disabled. I usually recommend customers place a pull up resistor (can be like 10k) on R if this is expected to occur.

    Similar feedback on D, if customer's MCU/processor powers up and the TX line is high-Z (before it is initialized) then D can float. I usually recommend a pull up resistor on D if customers think this is a potential concern. 

    EDIT: lastly, this device is older and we usually recommend our newer THVD devices like THVD1550 or THVD1450. 

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 40 points

    We updated the schematic design in this way. Is this correct?,

  • +1 in reply to Michael Soldierram
    TI__Guru 72751 points

    Hi Michael,

    Looks okay to me now. 

    For the pullup/pulldown resistors on the A/B side. Make sure only one node is populated with the resistors. The other nodes should be do not populate. 

    -Bobby