Aucbvax.6280
fa.info-terms
utcsrgv!utzoo!decvax!ucbvax!info-terms
Wed Feb 24 16:13:41 1982
Lear Sieglar ADM-3A quirk
>From decvax!duke!unc!mcnc!taylor@Berkeley Wed Feb 24 16:10:24 1982

This is one of those things which nobody documents, but can cause all grades
of problems in some isolated circumstances.  We have been running Lear
Sieglar ADM-3A terminals for years with relatively few problems.  Recently,
however, we installed a Timeplex stat mux at one of our sites (NCCU) which
had a cluster of ADM-3A's which were previously accessing services with
phone couplers.  All 3A's were working fine.

When the 3-A's were connected to the stat mux, which, incidently, was attached
at the host to a Develcon Dataswitch, some, not all, of the terminals would,
immediately after receiving the 'Request:(cr)(bel)' prompt from the host,
start sending a large (~100) number of space characters!  Needless to say,
the dataswitch considered this to be garbage, and the terminal was never
able to connect.  To make a 4 month story relatively short, we, and Timeplex,
changed EVERYTHING.  We replaced muxes at both ends. We replaced dataswitch
modules.  We checked the terminal on other services.  Everything worked
beautifully alone, with lots of other equipment in the network working also,
but there was something in the combination that was not working.

The first big break came Monday afternoon when I changed the phone coupler
which i had been using with my ADM-3A for a direct connect modem.  When I
called the dataswitch, I got the same results that I had gotten through
the mux.  Same story when I called one UNIX system, but fine results with a
different system with a different logon banner.  The crucial parameter turned
out to be having a bel (cntl-g) in the logon banner.

UNDOCUMENTED, BUT TRUE - Lear Sieglar confirmed that if a control-G is sent
when pin 22 on the EIA interface has a voltage (plus or minus) on it, this
is interpreted by the ADM-3A as an internal test code for which it will respond
be sending out a number of spaces.  The cables used in this case (to the mux)
included pin 22 (ring indicator).  The timeplex stat mux and the direct-
connect modem had pin 22 active, as they should.  since a phone coupler
does no know about auto-answer, pin 22 was no active so the terminal worked
fine.  Why the ADM is like this, i don't know, but I sure wish they had
documented it.

(It seems that the cntl-G had to be part of an initial connect sequence -
maybe it even had to be while ring indicator was high.  Also, it seemed to
not affect some ADM-3A's at all.  Very Strange.)

If you have found similar quirks with other terminals, please tell us about
them.  Maybe this will help you avoid all the hours I spent on this one.

Steve Taylor

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