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SN65C1167E: Data collision

user6101857
Prodigy 40 points
Part Number: SN65C1167E

Dears,

Communication between boards using SN65C1167EPW.
Under certain conditions Receive abnormal data.

When I investigated it,
it was in the state of the attached file(schematic-SN65C1167EPW.jpg ).
(Abnormal data occurs when SW1 is ON.)

Below are the questions.

Q1.In the attached circuit diagram, when SW1 is ON,
What waveforms are received on 1R and 2R of IC-B.

Q2.Actual 1A and 2A became like the attached oscilloscope waveform(OscilloscopeWaveform.jpg).
Is it as expected?

When the 1D and 2D logic of IC-A is in the attached file(schematic-SN65C1167EPW.jpg ) state,

(IC-A 1D is Drive-L,IC-A 2D is Drive-H)
Pulses such as 90deg phase difference pulses continuously enter the IC-B side.
(The counter circuit after IC-B counts.)
However, if the combination is different from the attached file(schematic-SN65C1167EPW.jpg ) state,
(IC-A 1D is H,2D is H. IC-A 1D is L,2D is L. IC-A 1D is H,2D is L.)
It does not become a pulse like a 90 ° phase difference pulse.
(The counter circuit after IC-B does not count.)

Q3.Why is the attached file(schematic-SN65C1167EPW.jpg ) combination
Will continuous 90 ° phase difference pulses be output?

Best regards,
Kanetomo Nozaki

  • 0
    TI__Mastermind 25705 points

    Kanetomo,

    When the driver of both sides are turned on (DE=H) and the input logic are opposite, the driver will fight with each other. One side tries to pull the bus high while the other side drags it low. The bus voltage could end up somewhere in middle due to the strength of the transceivers. RS-485 is a multi-drop system, which means one master and multiple receivers are allowed in the network. Please let me know if you have more questions.

    Regards,

    Hao

  • 0 in reply to Hao L
    Prodigy 40 points

    Hello Hao,

    Thank you for your answer.

    "The bus voltage could end up somewhere in
    middle due to the strength of the transceivers. "
    In the state of
    (Assuming that SW1 is ON)
    What happens to the 1R and 2R logic on the IC-B side of the drawing?


    Also,
    Schematic
    For
    IC-A side 1D: rive-L,
    2D: Drive-H,
    What happens?
    What happens to the 1R and 2R logic on the IC-B side of the drawing?

    Regards,
    kanetomo

  • 0 in reply to user6101857
    TI__Mastermind 25705 points

    Kanetomo,

    If both sides drive the bus the same way (H or L), the receivers of both sides work normally. If two sides fight each other, the receivers (1R/2R) output would be undetermined, especially when the bus voltage is near the threshold of the receiver. It's not recommended to use the transceivers this way, since the drivers work in the region similar to short current. Please let me know if you have more questions.

    Regards,

    Hao