Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mandrill!gatech!ncar!ames!ucsd!ucsdhub!esosun!seismo!uunet!iscuva!jimc
From: jimc@iscuva.ISCS.COM (Jim Cathey)
Newsgroups: comp.sys.mac
Subject: Re: Advice re. Terminal Emulator
Message-ID: <1723@iscuva.ISCS.COM>
Date: 11 Jul 88 16:07:22 GMT
References: <447@esquire.UUCP> <46100174@uxe.cso.uiuc.edu> <2275@wiley.UUCP>
Organization: ISC Systems Corporation, Spokane, WA
Lines: 26

In article <2275@wiley.UUCP> david@wiley.UUCP (David Hull) writes:
<<<Referring to Mac+ serial port>>>
>Pins 1 and 2 can be used for flow control, though pin 1 is labeled DTR,
>which you wouldn't normally expect to use for flow control.  The Mac

In fact, DTR is the more correct signal (choosing between RTS & DTR) to
use for input flow control.  RTS is Request-to-SEND, and is used when
turning around half-duplex lines.  DTR is Data-Terminal-READY, and
viewed in that light works well as "I'm ready to receive." Some serial
chips have additional logic to flip RTS at the right time at
end-of-transmission (Zilog SIO) and thus don't lend themselves to using
RTS for input-side control in a full- duplex environment for async comms.

I believe that when Zilog did the SCC they removed this handy RTS feature
because altogether too many customers wanted to use RTS for input flow 
control.  This makes writing a properly timed half-duplex async comm
harder for the SCC than for the SIO.  

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