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From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: help on serial port comm (jinu)
Date: Tue, 22 Oct 2002 18:54:19 GMT
NNTP-Posting-Date: Tue, 22 Oct 2002 11:54:19 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
jinu john wrote:
> we need to interface a photo sensor to the serial com port.we r new to
> this area so we have no idea!
> 1) IS it possible to send an external pulse of say 6V directly on the
> comm port?
> or do we need to design ckts for it.
> i was told that no external signal are fed to comp as that will
> damage the motherboard.and was asked to design a ckt that will switch
> one signal from one port of RS232 say TD to RD itself.and write a DOS
> based PRogram to detect it.
> i want to get interrupt from this sensor which will call a EXE in VB.
> as RS232 reqiures both negative and +ve V (-3 to -15)as 1 and
> (3to15)as 0 how do generate this pulses.please help me in the ckt
> diagram.and also tell me what precautions do ineed to take before it
> is safe to connect to pc.
> where can i get details to write the DOS programs or drivers?
> thank u
Look at the software for standard COMM support, then at the specs for
This way you will know what can (and cannot) set the IRQ flag.
This will guide you as to which pin(s) you need to activate, as well
as what software will be needed to handle the result.
BTW, RS232 signals are at minimum +3V for logic low (false or zero),
-3V for logic high (true or one).
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