Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mcdchg!motmpl!ron
From: ron@motmpl.UUCP (Ron Widell)
Newsgroups: comp.dcom.lans
Subject: Re: RTS/CTS flow control
Summary: don't stop in the middle
Keywords: uarts
Message-ID: <1259@motmpl.UUCP>
Date: 16 Jun 89 05:09:21 GMT
References: <5137@charon.unm.edu> <May.26.13.18.36.1989.214@ron.rutgers.edu> <May.31.13.57.52.1989.361@ron.rutgers.edu> <5187@b11.ingr.com> <1989Jun6.163942.15568@utzoo.uucp> <32466@bu-cs.BU.EDU>
Reply-To: ron@motmpl.UUCP (Ron Widell)
Organization: Motorola Semiconductor, Minneapolis, MN.
Lines: 34

In article <32466@bu-cs.BU.EDU> kwe@buit13.bu.edu (Kent England) writes:
<	In the context of full duplex interfaces RTS/CTS is hardware
<based flow control and I know that to be true in the course of
<application, having used it repeatedly over the years when software
<flow control did not work for one reason or another.  Of course, some
<interfaces use CTS to mean the same as CD or DSR.  The vendor has to
<cooperate a little here.
<	So, if you will accept this premise we can move the discussion
<on to the important issue of, when hardware flow control is activated,
<must the other side stop immediately, or should we allow the rest of
<the bits in the ASCII character in transit to come thru?  :-)  Sound
<like a fun problem to debug?  One reason I prefer s/w flow control,
<the argument about stopping in the middle of a character doesn't
<usually arise.
<
<	Kent England, Boston U

On every uart of which I am aware, the CTS input is an enable for
transferring the transmit buffer to the shift register. When CTS
is true, the character in the transmit buffer will be loaded into
the parallel load shift register after the last bit (plus the stop
bit[s]) has been shifted out. When CTS is false, this parallel load
will be disabled, but the operation of the shift register will not 
be affected.
Things can certainly change when synchronous protocols are involved,
e.g. the hardware handshake *could* (but usually doesn't) stop the
clock.
BTW, why must the characters be ASCII :-)?

-- 
Ron Widell, Field Applications Eng.	|UUCP: {...}mcdchg!motmpl!ron
Motorola Semiconductor Products, Inc.,	|Voice:(612)941-6800
9600 W. 76th St., Suite G		| I'm from Silicon Tundra,
Eden Prairie, Mn. 55344 -3718		| what could I know?