Ashok Kumar wrote:
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The Lm 339 output pin will not swing both power supply side.The output of lm339 is NPN transistor of open collector you will get the out put only -ve supply.


i designed a circuit using 339 that means i know how it functions. i stated it swings bith side that means it swings both side, infact i placed a pull-up at the output, thats no problem. any way instaed of understanding my problem u gave me the link of 339 datasheet. my problem is safe limit of P3 io pin for Vil is -0.5 v and i cant get a diode of voltage drop less than 0.6 volts. so is it permisibble practically (if anyone exprerimented) -0.7 v at an p3 io pin.


abhishek