piclist 2001\09\09\090726a >
Thread: Simple RS232 hardware
face BY : mike@spamBeGonewhitewing.co.uk

On Sat, 8 Sep 2001 09:39:36 -500, you wrote:

>> I'm sure this must have been covered before but a search of piclist.com
>> failed to find anything... Anyway what would you recommend as the
>> simplest/minimal hardware RS232 interface for use between a PIC and a modern
>> PC? This is *not* for a production product I would just like to be able to
>> include a very cheap interface on a home project for occasional
>> diagnostic/config use. Can I get away without using a MAX* converter? What
>> are the pros/cons? What would be your suggested circuit?
>For one-off, home projects, I'm in the "resistor-to-PIC" crowd.  I've used it a dozen or so times with no problems...  but of course people are right, it's not true EIA-232, it's not guaranteed to work, etc etc.  Truth is it will work in the vast majority of cases, but I'd probably not use it in a production device.  I have seen it done in commercial products though, often.  Mice come to mind.
If you KNOW that you will be talking to a PC and not some other serial
device (which may also use nostandard levels), and the cable length
isn't too long (like it's a widget that plugs straight onto the PC
socket, or has a shor (<2M) captive lead, and the baudrate is
sensible, and you're not trying to pull too much power from the
control lines, you should have no hesitation about doing this in
production. It works, period.
>Pros:  Dirt cheap.  Extremely simple.  Dirt cheap.
>Cons:  You HAVE to do bit-banged comms, since there is no way to invert UART data.
> Also not precisely to PIC datasheet specs.  Not enturely true - the data shhets do specify the maximum input clamp
current - although the data I have in front of me lists it in the
'absolute max' parameters, it is entirely reasonable to infer than
operation a couple of orders of magnitude below this is fine.
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<vsfkpt8j6a9gebuh6hhq49tje3qpste61b@4ax.com> quoted-printable

In reply to: <3b9a2da8030570.69010135@botkin.org>
See also: www.piclist.com/techref/microchip/ios.htm?key=rs232
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