Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!amdcad!ames!pasteur!ucbvax!NIHCU.BITNET!RAF
From: RAF@NIHCU.BITNET ("Roger Fajman")
Newsgroups: comp.dcom.modems
Subject: Re:  EIA Flow Control
Message-ID: <8802222331.AA03700@ucbvax.Berkeley.EDU>
Date: 22 Feb 88 22:48:48 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 19

> As has been pointed out, there are many, many ways to make a null modem.
> The cross of 4 and 5 is 'best' when you have devices which implement
> the so called "EIA Flow Control" (aka hardware flow control).  Here,
> CTS controls the flow from DTE to DCE, RTS controls the flow from
> DCE to DTE.  In this scheme, there is no longer any correlation between
> the assertion of RTS and the reply with CTS.

Interesting.  What are some examples of devices that work that way?
I haven't run across any, while I have seen a lot that use DTR.

Does the RS-232C standard really cover this use of Request To Send?
I haven't read it lately, but judging from the name of the pin, I
suspect not.  If that is true, then it is something of a misnomer to
call it "EIA flow control."  The normal use of RTS/CTS that the DTE
brings up RTS when it wants to transmit and receives CTS from the
DCE when it is ok to do so.  It's important with half duplex modems.

Yes, of course there are many ways to make a null modem.  What works
in one case may not work in another.