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need help with ADM2484E

Yurik
on Nov 3, 2011

Have received a problem at use ADM2484E - the starting bit turns out with  "step". The circuit drawing and signal photo in the appendix. In the photo:

- blue signal (3) - transmission enable - pin 5 DE ADM2484E

- green (2) - TxD signal on 6 pin of ADM2484E

- yellow (1) - RS485 line signal (DATA+ pin 14 ADM2485E)

Thanks!

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    •  Analog Employees 
    on Sep 3, 2015 8:07 PM over 5 years ago

    Hi Ivan,

    More recent investigation of similar issues shows that this can occur only at initial communication when not only is the bus unterminated, the cable is short, and the other node powered by 5V, but there is no common wire connecting ADM2484E GND2 and the ground of the other node, and finally the scenario also includes the 5V node having pull-up and pull-down resistors.

    This is simply a scenario where there is a delay in the ADM2484E driver asserting the bus state. There are several options for avoiding this:

         a) termination

         b) larger resistor between A and B

         c) add a common wire between GND2 on ADM2484E and the other node

    We haven't tested 10k from B to GND2.

    This isn't a general 3.3V to 5V issue, it's only at initial comms, when all 4 other conditions are present (unterminated bus, short cable, no common, pull-up and pull-down at the other node).

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    •  Analog Employees 
    on Sep 3, 2015 8:07 PM over 5 years ago

    Hi Ivan,

    More recent investigation of similar issues shows that this can occur only at initial communication when not only is the bus unterminated, the cable is short, and the other node powered by 5V, but there is no common wire connecting ADM2484E GND2 and the ground of the other node, and finally the scenario also includes the 5V node having pull-up and pull-down resistors.

    This is simply a scenario where there is a delay in the ADM2484E driver asserting the bus state. There are several options for avoiding this:

         a) termination

         b) larger resistor between A and B

         c) add a common wire between GND2 on ADM2484E and the other node

    We haven't tested 10k from B to GND2.

    This isn't a general 3.3V to 5V issue, it's only at initial comms, when all 4 other conditions are present (unterminated bus, short cable, no common, pull-up and pull-down at the other node).

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