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Path: utzoo!utgpu!water!watmath!clyde!rutgers!seismo!uunet!pcrat!rick
From: rick@pcrat.UUCP
Newsgroups: comp.dcom.modems,news.sysadmin
Subject: Re: Hardware Protocol
Message-ID: <374@pcrat.UUCP>
Date: Sat, 22-Aug-87 07:22:46 EDT
Article-I.D.: pcrat.374
Posted: Sat Aug 22 07:22:46 1987
Date-Received: Sun, 23-Aug-87 11:04:59 EDT
References: <192@caeco.UUCP> <2849@phri.UUCP> <1103@laidbak.UUCP> <1172@geac.UUCP> <419@piaget.UUCP>
Organization: PC Research, Inc., Tinton Falls, NJ
Lines: 32
Keywords: RS-232 CTS flow-control
Xref: utgpu comp.dcom.modems:765 news.sysadmin:297

In article <419@piaget.UUCP>, jc@piaget.UUCP (John Cornelius) writes:
>  >In article <2849@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>  >>
>  >>	Arghhhhh!  Maybe the reason Sun's RS-232 ports don't do RTS/CTS
>  >>handshaking is because if they did, it wouldn't be RS-232.  As defined in
>  >>the standard, RS-232 has no flow-control. 

True enough, the original use of RTS/CTS is for modem turnaround in a
half-duplex environment.  However, this also gives you one direction flow
control (The 'DCE' side can stop the 'DTE' side from transmitting by
deasserting CTS).

> The Systek MTI-16 which is used on the Sun-3/160 does indeed
> observe rts/cts flow control and it says so in the manual.  I
> have recently connected a plotter to one port of ours and it
> works marvelously.  

Plotters, usually, only need one direction flow control.

However, what I think we were originally discussing is the defacto standard
of using RTS/CTS in a *full duplex* environment to provide *two way* flow
control.  In this scheme, CTS is still used by the DCE to flow control
the DTE.   However, there is no relationship between RTS and CTS anymore.
Instead, RTS is given a new meaning.  When the DTE wants to flow control
the DCE, it deasserts RTS.  Think of RTS as "Receiver Ready" and it
makes good sense.  I don't know how many vendors implement this in
their products, but I know that AT&T does in some of its product line.

-- 
	Rick Richardson, President, PC Research, Inc.
(201) 542-3734 (voice, nights)   OR   (201) 834-1378 (voice, days)
		seismo!uunet!pcrat!rick