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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.unix
Subject: Re: rts/cts - a tutorial on flow control
Message-ID: <5634@utzoo.UUCP>
Date: Mon, 27-May-85 13:57:49 EDT
Article-I.D.: utzoo.5634
Posted: Mon May 27 13:57:49 1985
Date-Received: Mon, 27-May-85 13:57:49 EDT
References: <388@gitpyr.UUCP> <1345@amdcad.UUCP>, <879@sdcsvax.UUCP> <5620@utzoo.UUCP>, <429@gitpyr.UUCP>
Organization: U of Toronto Zoology
Lines: 31

> > ...  (What *were* CTS and RTS meant for, you
> > ask?  For turning around half-duplex modems.)
> 
> Halfway correct.  CTS/RTS has slightly different meanings when operating either
> under half-duplex or full-duplex mode.  To quote from the EIA RS-232-C
> standard...
> 
> 		...
> 		The ON condition together with the ON condition on
> 		interchange circuits RTS, DSR and, where implemented,
> 		DTR, is an indication to the DTE (data terminal equipment)
> 		that signals presented on circuit TD (transmit data)
> 		will be transmitted to the communication channel.
> 
> 		The OFF condition is an indication to the DTE that
> 		it should not transfer data across the interface
> 		on circuit TD."
> 
> That last paragraph has the phrase 'flow-control' written all over
> it...

Unfortunately, taken in conjunction with the preceding paragraph it
doesn't, since said preceding paragraph is quite clear about the role
of CTS -- it tells you whether you are connected to the communication
channel, i.e. whether RTS has succeeded yet.

Whether or not the standard says it out loud, half-duplex line turnaround
is very definitely what CTS and RTS were *intended* for.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry