@ KlausST,
i tested again the line voltage and it is 4mV between line and ground. but this level is considered low. please see attached picture.
@gauravkothari23,
as i have come to know i incorrectly said that i have a pulldown resistor. i didn't see that you meant a pulldown/pullup resistor on the cmd signal line. i have pulldown resistor connecting to a switch which is used to put the cmd signal low on pin 12 of the micro(attached picture) which i meant to say.
i didn't understand why a pullup or pulldown resistor on the signal line could do the job. although the signal line micro pin is output and low in the default, i have configured it as output and high. also i didn't understand how i can put transistor to put the line into logic 0 or ground. i guess with transistor it can be put to ground voltage. could u explain a bit more. perhaps tell where i have to put the transistor in the shown figure(i mean the base, emitter and collector). any additional info would be great.
any other suggestion would be helpful.
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