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ADM2867E not giving the output data correctly

Category: Hardware
Product Number: ADM2867E

Hello All,

I am new in this forum, please let me know if I need to do certain things, or have some mistakes in asking question.

Currently I am using https://www.mikroe.com/rs485-isolator-2-click which is based on ADM2867E and has schematics here https://download.mikroe.com/documents/add-on-boards/click/rs485_lsolator_2_click/rs485-isolator-2-click-schematic-v101.pdf , and I am currently facing a problem.

My purpose is to have a communication between MCU with 3.3V and RS485 devices on different voltage system and ground (Isolated system)
I have connected RE/DE together as I am using Half Duplex for this communication

I did not receive any reaction from the RS485 device, so I was troubleshooting the MikroE board when I found out that there is no output on A B side

If you see the picture above the color is listed as below:
Yellow - B
Purple - A
RE/DE - Blue
TX - Green

From the picture above, the TX is not translated at all to the other side of RS485 A B.
After I scope it several times, I also found out that some of the signal actually passed through

Ignore the blue and green as I forgot to connect it this time

About the Board itself, I am connected the YZ and the AB as it is half-duplex and connected J7 J8 and J9 in the isolator schematics (link on top)

Please help me on my problem.

Thank you!

  • Hello, thanks for the detailed info on the problem. 

    Can you confirm that the J3 0ohm jumper is connected, the J2 jumper is disconnected, and you are applying the DE/RE signal to the RE pin (RTS) of the Mikroebus connector? This will confirm that the signals you are observing on the oscilloscope are actually making it to the DE and RE pins of the ADM2867E. 

    This board does not have any probe points for DE/RE , where are you taking the oscilloscope measurements from?

    If this is confirmed, as the next step in the debug, I would recommend checking that the power supplies on the ADM2867E are all powered up correctly. 

    Regards,

    Neil

  • Hello Neil,

    Thank you for replying
    I am actually not using mikrobus connector, I am connecting directly to RE/DE from my microcontroller and I can probe it in my testing board.
    The board itself has J2 disconnected, and J3 connected, I have confirmed that.

    Power supply should be correctly applied since actually there is 3.3V on the A B side, this is according to the power supplied at VCC 3.3V.
    If you see the picture, the problem is AB does not give correct binary data like the TX, instead it just stay at that voltage (A high, B low) when TX sends data

  • Thanks for your reply,

    I have tested an MikroE board here today and it appears to be working correctly. 

    I'm not clear on what the cause of this issue is, though I agree that from your oscilloscope plots the A and B outputs appear not to be responding correctly to the TxD input. 

    I would recommend a few steps to ensure the measurement setup is correct, 

    • Have you measured 3.3V power supply on the AB side with a DMM or an oscilloscope probe? As you have mentioned, as VCC is 3.3V, then VISO should equal 3.3V, but it is still worth confirming this with lab equipment
    • I would recommend taking all measurements if possible on the board rather than on the microcontroller board. For example, if there is an issue with the ground lead connection between your MCU board and the MikroE board, the signals measured on the MCU board do not reflect what is seen by the ADM2867E

    Regards,

    Neil