http://www.8051projects.net/ Learn to make simple microcontroller projects, pic, 8051, avr and arm projects. download 8051 projects, tutorials, libraries, sample codes. join the microcontroller discussion forum and ask doubts regarding electronics. the best source for 8051 over internet. en-gb 2008-12-01T23:51:56-08:00 contact@nospam.com hourly 1 2000-01-01T12:00+00:00 http://www.8051projects.net/forum-t9535.html 2008-12-01T23:51:56-08:00 hey just a curious question, does a -ve 5v at the microcontroller pin do any damage to it?? im using a zero crossing detector as an interrupt & im gettin square pulses of 10vpp http://www.8051projects.net/forum-t9535.html 2008-12-01T23:51:56-08:00 Chiru Dear Ved, use a diode to get the +ve half for zero crossing detection.Controller pins, in general, are meant to operate in the positive side with respect to GND. A 10% in the reverse polarity may destroy the chip. There may be exceptions for a particular controller and particular pin.Consult the Absolute Maximum Ratings in the data sheet for that chip, to be sure. http://www.8051projects.net/forum-t9535.html 2008-12-01T23:51:56-08:00 Ved k thnx dude, simple solution i knw, just found out an hr back tht the -ve voltage causes damage....