From: "Alexei A. Frounze" <alex DOT fru AT mtu-net DOT ru>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: com1 programming .... a lot of question
Date: Fri, 19 May 2000 03:36:15 +0400
Organization: MTU-Intel ISP
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

If you take a look at my program that works with COM port, you may notice it
uses TxD and RxD only.

Btw, does BIOS assume more than just these 2 signals (read/write) with
null-modem cable? Neither RB Int list nor TechHelp nor HelpPC says how many
signals are in use in BIOS service functions.

-- 
Alexei A. Frounze
-----------------------------------------
Homepage: http://alexfru.chat.ru
Mirror:   http://members.xoom.com/alexfru

Jason Green wrote:
> 
> Eli Zaretskii <eliz AT is DOT elta DOT co DOT il> wrote:
> 
> > On Thu, 18 May 2000, Alexei A. Frounze wrote:
> >
> > > Btw, I usually connect 2nd and 3rd pins of the serial cable/connector in
> > > order to test I/O on a single computer. Could this situation be problematic
> > > for BIOS?
> >
> > I don't think so, but I'm not really a hardware person.  Anybody?
> 
> I don't know about BIOS functions, but only looping pins 2&3 (Tx/Rx)
> could definitely lead to different behaviours between programs.
> 
> If some code is looking for a handshake line to be asserted then it
> could appear to hang, if some other code ignores the handshake lines
> then it will appear to work but could drop bytes.
> 
> Loop-back the handshake lines, DTR-DSR and/or RTS-CTS.  And make sure
> you also assert the outgoing handshake lines DTR & RTS.