Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.dcom.modems
Subject: Re: Connecting a TrailBlazer to a Sun 3/280
Summary: DZ11
Message-ID: <5445@cit-vax.Caltech.Edu>
Date: 15 Feb 88 06:32:27 GMT
References: <218@coherent.uucp> <3238@cbmvax.UUCP>
Distribution: comp
Organization: California Institute of Technology
Lines: 29

In article <3238@cbmvax.UUCP>, grr@cbmvax.UUCP (George Robbins) writes:
>    For example, DEC DZ11's don't support 19200 baud.

They do on 4.2bsd.  DEC doesn't document it because the rate is not
divided exactly (it's actually 19600 baud) but it's close enough for
many devices.  The 64-character silo provides enough buffering for
only 1/30 of a second, so any kernel printf will cause dropped
characters, but that's true of any serial interface for a vax.

The thing that makes it useless for high-speed devices like
Trailblazers is the lack of CTS flow control.

The Able DH/DM is one of the few Unibus serial interfaces that
provides CTS, but because it uses a DZ11-compatible distribution
panel (which doesn't have a wire for CTS) this is done in a very
kludgey way.  At the DH/DM and at the panel, you jumper RI and CTS
together.  This sacrifices the RI signal, but 4.2bsd doesn't do
anything with that anyway.  It's a pain to configure, but works
quite well, at least with our U-B terminal switch.

The 256-byte silo helps.  The Emulex CS21/H has a 256 byte silo
too, but the factory settings restrict it to 64 bytes for DEC
diagnostic compatibility, so check the switches.  The CS21/H
lacks CTS, so it will not fare much better than the DZ11.

Able DH/DM's can sometimes be bought cheap from VMS sites/dealers
that have acquired some by buying an old Unix vax.  I have 3.

Don Speck   speck@vlsi.caltech.edu  {amdahl,ames!elroy}!cit-vax!speck