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ISO3082: The feedback waveform is missing the negative edge

user4637774
Intellectual 550 points
Part Number: ISO3082

Tool/software:

We use ISO3082DWR in our new project.

Symptom: We send the waveforms on the left of the following picture to RS485 A and B through the computer, and the feedback from RS485 A and B is like the waveforms on the right of the following picture.
Problem: The RS485 feedback waveform has less negative edges, and the amplitude of the waveform is reduced a lot.  Help analyze what caused the problem，thanks.

The circuit design is as follows: R101  120Ω was removed , the R100 and R104 were changed to 0Ω, and the R97 and R105 pull-down resistors were removed during the test.

  • 0
    TI__Mastermind 29415 points

    Hello, 

    Thank you for reaching out. I would like to understand more about the intended use case of your application. The schematic shows a node called UART_RX connected to receive (pin3) and a UART_TX connected to RE and DE. RE and DE are the enable and disable for the driver and receiver (pin 13 and pin 12). Normally UART_TX nodes are connected to the driver (pin 6) to transmit signal on the RS485 bus. Currently the circuit would only be able to act as a receiver. Is this the intended use case? 

    If this is the intended set up then the ISO3082 would not be able to feedback or respond to any signal received on the RS485 (A and B) pins. 

    Best,
    Andrew