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From: callen@ada-uts.UUCP
Newsgroups: net.arch
Subject: Re: clear screen on a IBM 327x terminal
Message-ID: <7900004@ada-uts.UUCP>
Date: Wed, 18-Dec-85 10:19:00 EST
Article-I.D.: ada-uts.7900004
Posted: Wed Dec 18 10:19:00 1985
Date-Received: Sat, 21-Dec-85 05:15:19 EST
References: <1764@utcsri.UUCP>
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Nf-ID: #R:utcsri:-176400:ada-uts:7900004:000:1762
Nf-From: ada-uts!callen    Dec 18 10:19:00 1985


>***** ada-uts:net.arch / utcsri!hofbauer /  6:23 pm  Dec 11, 1985
>This may not quite be the right group to post this query to, but it is
>the closest approximation I could find. How does an IBM 4341 or like
>machine running under CMS send a signal to an IBM 327x terminal to clear
>the screen. I hope it's some kind of escape sequence...if so, what is it?
>The local gurus are anything but and so haven't been able to help me.

Hmmm...do you mean "how does the hardware work?" That's easy. There are
*TWO* ways to clear the screen. One is by writing to the tube with an
"erase-write" command, which clears the screen before writing your new
data to it. The other is by including the following sort of "order
sequence" in the data stream (note - I have macros to do this, but
they are NOT supplied by IBM):

          SBA (1,1)            Put cursor in upper left hand corner
          RA  (24,80),X'00'    Fill screen with nulls (assumes 24x80)

SBA means "set buffer address", and moves a sort of invisible cursor
around in the 3270 buffer. RA means "repeat to address", and it fills
the buffer with the supplied character from the current buffer address
to the supplied address. Here we fill it with null characters (which
erases the screen).

All this stuff is decribed in the following IBM manuals:

GA23-0059 IBM 3270 Data Stream Programmer's Reference
GA23-0061 IBM 3274 Control Unit Description and Programmer's Guide

Unfortunately I don't know much (like zilch) about CMS so I don't
know if there is an easy way to have CMS do this for you. Hope this helps.

-- Jerry Callen     Intermetrics, Inc.     Cambridge, MA
   ...ihnp4!inmet!ada-uts!callen

with BOILERPLATE;
procedure Cover_My_Butt is
   use BOILERPLATE;

begin
   Standard_Disclaimer;
end;