I want verify 2nd case of the below truth table of MAX485 IC (RS485). Please see in red color.enter image description here

Is my circuit correct ? I have connected RE,DE and A-B to GND for making it LOW.I have connect DI to GND also just to avoid floating connection. However LED still unexpectedly blinks. why?


simulate this circuit – Schematic created using CircuitLab

what is wrong in my cicuit?


  • \$\begingroup\$ This is basically same as your previous question? \$\endgroup\$
    – Justme
    Commented Oct 31, 2020 at 16:42

1 Answer 1


Since both A and B are 0V, 0V-0V=0V difference between them. The difference does not exceed threshold of logic 1 or logic 0 (+0.2V or -0.2V) so the fail-safe mechanism keeps the RO high.

  • \$\begingroup\$ how can i create difference of A-B = 0.2v between pins A and B? \$\endgroup\$
    – Ravi
    Commented Nov 1, 2020 at 8:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.