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From: robin@uhunix1.uhcc.Hawaii.Edu (Robin Amano)
Newsgroups: sci.electronics
Subject: Re: RS232 Flow Control
Message-ID: <10276@uhccux.uhcc.Hawaii.Edu>
Date: 13 Nov 90 23:41:54 GMT
References: <1990Nov10.013730.28838@julius.cs.uiuc.edu> <1990Nov13.184339.4756@zoo.toronto.edu>
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In article <1990Nov13.184339.4756@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <1990Nov10.013730.28838@julius.cs.uiuc.edu> totty@flute.cs.uiuc.edu (Brian Totty) writes:
>>	I want to send flow control information back to a sender across
>>	an RS232 serial cable.  What signal is appropriate for this?
>
>There is no, repeat no, standard convention for this.  You have to find
>out exactly what your sender is willing to accept, if anything.  It is
>common to use CTS and RTS for this.  DSR and DTR are also used.  None of
>these lines was originally intended for this purpose.

Those used above are usually used for hardware handshaking, where you toggle
the line high or low.  For this you would normally have to use 4 wires (tx, rx
gnd, and a control line(like one mentioned above)).  Xon Xoff is another way
of sending flow control information using only 3 wires.  Because it is software
controlled you use only (tx, rx, and gnd).  Normally you would send a DC3 or
CTRL S to signal the computer to stop sending data, and a DC1 or a CTRL Q to
resume flow of data.


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