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Pramod • Apr 16, 2007

Input to parallel port

i want to input 8 bits to EPP port. I have tried using 74HC244, 74LS244, 74LS245 as buffers but then also i am observing problem of overloading.
If I connect 5V power supply to i/p then reading suceeds.
please help me..
maheshkrishnan • Apr 16, 2007
For serial and parallel port interfacing ,
go thru the site

RachaelP • Apr 16, 2007
The input voltage levels for a standard parallel port are TTL levels i.e. logic '0' <= 0.8V and logic '1' >= 2V so any TTL compatible 74xx245 should work fine. My guess is that you either have a problem with the control lines or you havent got the grounding good enough and the data lines arent reaching the correct levels due to ground bounce (i.e. there should be a good ground connection between your board's ground and the ground of the parallel port). For the control lines you should connect nIOR, nIOW or nWrite to the Dir pin of the 245 and then nDataStrobe to the En pin of the 245. I'm not sure which way the Dir pin is off the top of my head so make sure the selected direction (i.e A to B or B to A) is correct.

One more thing could be decoupling. You should put a 100nF cap very close to the Vcc pin of the 245 otherwise it may latch up. Also a larger 10uF might be of some use too.

Hope this is of some use.


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