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Thread: It's official: The Real-World Serial FAQ
www.piclist.com/techref/io/serials.htm?key=serial
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face BY : Russell McMahon email (remove spam text)



> On the other hand, if you aren't using the a/d convertor, an RS-232 input
> direct to an input pin via a suitable current limit resistor (I use 22k)
> works just fine.

This is completely true.
The minimum value of "a suitable ... resistor" is the question.
100 Mohm would quite possibly be suitable in most cases.
Higher may be in order on occasion :-)

Notwithstanding any number of good experiences to the contrary, RS232 plus
22k will absolutely definitely certainly catch you out *sometimes* YMWV. On
my very first RS232 plus PIC experience (but far far from my first
microprocessor experience) MyMdidV.

Any newbie, and anyone else who wants to spend their life working on
formally defined problems (such as may be found in true digital designs),
rather than non-deterministic ill defined & infinitely variable problems,
are advised to stick to the manufacturers spec sheets so that the processor
remains a true digital part in areas were it is intended to be so.

Ask me how I know :-(

More anon.

           RM

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