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SN65HVD3082 - not communicating

Atul Bhakay
Genius 3205 points
Other Parts Discussed in Thread: SN65HVD3082E

6404.RS485 Modbus.pdf

Hi,  

We are using IC ADM2483 for modbus communication in our existing Multi Function Meter. 

Now we made the PCB layout using IC SN65HVD3082E.

We implimented application note of  SN65HVD3082E in our existing  Multi Function Meter. 

Voltage at each pin is matching with existing circuit. 

But there is a problem in communication. 

Here we are attaching the circuit diagram of  RS485 modbus using IC  SN65HVD3082E .Please guide us earliest.

Regards  Atul Bhakay

  • 0
    TI__Genius 14015 points

    Hi Atul,

    Can you please take some oscilloscope captures showing the D and R, A and B pins? That will help us determine what is wrong. 

    A few things that I noticed looking at your schematic:

    1) The 10k termination resistor is much larger than normal. During bus idle, it is limiting the differential voltage to Vcc/3 (as opposed to if you had no termination resistor and only 10k pull-up and pull-down, the bus voltage would be ~Vcc). When driving data onto the bus, it is weak enough that it will be over driven. Basically, the 10k termination resistor is doing nothing.

    2) What are the capacitors on the bus for? They don't appear to be configured as a filter, and will only serve to slow the bus down.

    Let me know about those scope shots,
    Jason Blackman 

  • 0
    Genius 3205 points

    Hi All,

    The issue has been resolved

    Regards Atul Bhakay