piclist 2001\01\19\160214a >
Thread: Reading Outputs as Inputs
www.piclist.com/techref/microchip/ios.htm?key=input
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face BY : Dwayne Reid email (remove spam text)



At 09:57 AM 1/19/01 +0000, Alan B. Pearce wrote:
> > I'm surprised at this! With all the professionals
> > on this list, I have become used to the "never go
> > outside the spec" attitude, like never exceeding
> > clock frequency etc. I really don't like the idea
>
>Is it really that different to driving directly into the base of a transistor?
>The impression I have is most people on this list would do that to drive a
>relay
>or other high current load without a resistor between the output from the PIC
>and the base of the transistor - we get enough messages on the list about
>reading back the port state when doing this.

Nope - you missed the point in that discussion, which involved only the
open drain pin RA4.  It is quite legal and safe to use a pullup resistor on
pin RA4 and connect the pin directly to the base of a transistor (emitter
to ground).  The drawback in doing so is that R-M-W instructions read back
a logic 0 on RA4 - that is what the discussion was about.

dwayne



Dwayne Reid   <spamdwaynerspamTakeThisOuTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 17 years of Engineering Innovation (1984 - 2001)

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