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From: nichols@uwmacc.UUCP (Dennis Nichols)
Newsgroups: net.dcom
Subject: Re: hardware flow-control on a VAXen
Message-ID: <2184@uwmacc.UUCP>
Date: Mon, 5-May-86 14:32:17 EDT
Article-I.D.: uwmacc.2184
Posted: Mon May  5 14:32:17 1986
Date-Received: Thu, 8-May-86 06:58:00 EDT
References: <1747@sdcsvax.UUCP>
Organization: UWisconsin-Madison Academic Comp Center
Lines: 21

> Recently, whilst installing our Ungerman-Bass NIUs on one of the VAXen
> here at UCSD, I discovered that certain models of comm line multiplexors
> can do hardware flow control.  In particular, the Emulex CS-11 (which
> does a pretty good job of looking like a DH11) has a switch for each
> line located in the multiplexor panel that when turned on causes the
> UART transmitter to pay attention to Clear-To-Send. ... 
>
> ...  For most applications, this works extremely well.
> 
> 	Brian Kantor	UC San Diego

We purchased Emulex muxes with the hope of using this feature.  VMS
didn't like it because writes would timeout if Clear-To-Send was held
off too long.  Worse than that, the Emulex would sometimes lose
characters from a write with the switch in the 'use CTS' position.
Because of problem one we did not push too hard to get problem two
fixed (seemed to be a firmware bug having to do with length of line,
not with the CTS signal actual going low).  Emulex may well have 
corrected the situation by now.

Dennis Nichols  University of Wisconsin-Madison Academic Computing Center