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From: root@zswamp.uucp (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Hardware Flow Control - How does it work?
Message-ID: <105.2843277A@zswamp.uucp>
Date: 28 May 91 13:31:30 GMT
Organization: Izot's Swamp BBS (FidoNet), Kitchener, Ontario
Lines: 31

In a letter to All, Rob Stampfli (res@colnet.uucp ) wrote:

 >Generally, there seems to be two implementations of hardware flow control,

   I'd suspect that there are more, since many manufacturers have embellished 
the RS-232 standard to suit their own tastes.

 >  "However, in the full-duplex variations, RTS/CTS is used 
 >as a kind of
 >  throttle.  The signals have the opposite meanings than 
 >they do for
 >  half-duplex communications.

 >  "When a DTE device is able to accept data, it asserts pin 
 >4, Request to
 >  Send.  If the DCE is ready to accept data, it asserts pin 
 >5, Clear to
 >  Send.  If the voltage on RTS or CTS drops at any time, 
 >this tells the
 >  sending system that the receiver is not ready for more 
 >data...

   This is in fact how high-speed dialup async modems use the RTS and CTS 
lines.
 

--  
Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171)
root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root
602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553
"He who claims to know everything can't possibly know much" -me