View Full Version : Logical Limits

30th April 2005, 11:57
Hi everyone,

I have a question that I hope some will be able to answer.With pics you have Logical 1=5v or logical 0=0v.What it the threshold at which a logical 1 becomes a logical 0? and a logical 0 becomes a logical 1? I hope I make sense.Thanks for any advice. Sorry for posting this hereimages/icons/icon11.gif

Mark Rodgers
30th April 2005, 12:19
If you look under DC Characteristics in the Data sheet you will find "Input Low" an "Input High" voltage tables, for the 18f452 these vary dependant on the type of input pin you use and its mode, in general low is taken to be less than 200mv (in some cases 800mv) and the high is in general 700mv - 900mv (to supply), or (2v if a high level "zero" level.

There are quite a few variables such as temperature and supply voltage to take in to account.

30th April 2005, 12:21
Hi Mark,

Thanks for the info.I guess that it also veries with the pic.Thanks again.