sonar sensor interfacing with 89v51RD2

[niranjan_187]

I am using a sonar sensor with three pins.Two for power supply(5V dc) and one for signal(SIG).
I need to trigger the sensor first and then monitor the sensor for obstacle detection using SIG pin.How to make a port pin of my controller as input after triggering the sensor.If i write logic 1 on that pin,it shows as output is high.What shall I do.

 

[IanP]

If i write logic 1 on that pin,it shows as output is high.

And that's OK, as it’s a very weak internal pull-up that causes the pin to go "high", but it will by no means interfere with the sonar ..
Just write a "1" and this pin will act as INPUT ..

IanP