Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ames!oliveb!tymix!antares!jms
From: jms@antares.UUCP (joe smith)
Newsgroups: comp.sys.dec.micro
Subject: Re: Memory Location for Text Screen
Summary: It moves around all over the place
Keywords: memory map
Message-ID: <214@antares.UUCP>
Date: 20 Oct 88 07:10:40 GMT
References: <3847@homxc.UUCP>
Reply-To: jms@antares.UUCP (joe smith)
Organization: Tymnet QSATS, San Jose CA
Lines: 22

In article <3847@homxc.UUCP> dj@homxc.UUCP (Dave Jenkins) writes:
>I need to know how to access the Dec Rainbow's screen from machine language.
>Is screen memory mapped?  What are addresses?

Each line is stored at a different location in memory - all 24.5 lines are
stored as a linked list.  If you have ever seen the limited scrolling region
in use you'd understand why the lines cannot be stored in consecutive
locations in memory.  This is why fixed locations in RAM cannot be used
(unlike the IBM PC). 

The usual way to address the screen is via escape sequences.  For instance,
ESCape "[" "2" "4" ";" "8" "0" "H" "*" will put an asterisk in the lower
right hand corner (line 24, column 80).

There is a "fast-video" BIOS call for updating the screen quickly.
One place you can find a working example of this sort of code is in the
sources to the Rainbow version of MS-DOS KERMIT.  I think I might have
the CP/M and MS-DOS Tech Docs at work somewhere.
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