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THVD1520: The data received from slave is error code.

Moon Wang
Intellectual 1285 points
Part Number: THVD1520
Other Parts Discussed in Thread: SN65176B

Tool/software:

Hi Team,

My customer has a problem of the received data from salve. There are 6 slaves in the system and the data from last one (the most far from the master) is abnormal.

Below is the schematic:

U13 is changed to THVD1520 and the problem is not solved.

When they changed the master to another brand, the slave is normal, so the slave works.

Could you please review this schematic?

I'm not sure the level shift device could cause some problems.

BR,

Moon

  • 0
    Guru 316690 points

    How did you configure SW2 at all nodes?

    Please check the slave's USART2_TX signal, the signal at the D pin, the A/B bus lines, and the receiver's R pin with an oscilloscope. At which place is the signal not transmitted correctly?

  • 0
    TI__Genius 13502 points

    Hi Moon,

     

    Initially it seems to be that your configuration is not quite correct as there appears to be loss at the end of the bus. It is possible the competitor part has a higher driver spec, which is why it worked. 

     

    Several questions to help narrow things down:

    - First, can you confirm your termination resistor configuration (as Clemens mentioned)? The master and the slave that is furthest away from each other (i.e. the end nodes) should both have termination resistors. So SW2 should be on for only the end nodes, that should resemble this diagram:

     

    - Second, is there fail-safe networks on every node? Ideally there should be just one fail-safe network on an end node. Otherwise impedance matching becomes more complicated. 

     

    - Third, do you know what exact competitor device they used so I can see any different specs it might have? 

     

    Best,

    Ethan

  • 0
    TI__Genius 13502 points

    Hi Moon,

    Just following up in case you still need help. If you figured out the issue, feel free to mark this thread as resolved. 

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    TI__Intellectual 1285 points

    Hi Ethan,

    Really thanks for your reply.

    -There is a lot of noise and disturb on the signal. They tried a lot of solutions with different value of resistors that include termination resistors, but the issue is still not solved.

    -Not on every node. The issue is just on the end node.

    -the machine of another brand they tried is also used THVD1520. We consider it should use isolation because of the bad environment.

    Do you have other recommends? Thanks a lot.

    BR,

    Moon

  • 0 in reply to Moon Wang
    Guru 316690 points

    Please show an oscilloscope trace at the end node. If possible, compute A − B.

    If the noise has a higher frequency than the signals, you can add low-pass filters. Otherwise, you can use common-mode chokes (you already have them) or add shielding (I don't know what cables you're using).

  • 0 in reply to Moon Wang
    TI__Genius 13502 points

    Moon,

    Thank you for the additional information. An oscilloscope trace at the end node (subtracting A - B) as Clemens mentioned would be helpful. 

    Can you send me a photo of the device part markings at the end node (I am assuming it's an SN65176B)? I can check internally to verify if it any similar problems have been reported and to check whether it is a legitimate part. Sometimes counterfeit devices infiltrate the market.

    If you can provide the bus length and the data rate, that would also aide us in narrowing down any potential problems.  

    -Ethan