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From: mjs@ernie.Berkeley.EDU (Marc J. Sabatella)
Newsgroups: comp.sys.ibm.pc
Subject: Re: How to turn off cursor?
Message-ID: <21876@ucbvax.BERKELEY.EDU>
Date: Fri, 20-Nov-87 13:52:08 EST
Article-I.D.: ucbvax.21876
Posted: Fri Nov 20 13:52:08 1987
Date-Received: Sun, 22-Nov-87 16:09:09 EST
References: <2065@killer.UUCP> <5060014@hpccc.HP.COM> <3639@uw-june.UUCP> <428@cpsc6b.cpsc6a.att.com>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: mjs@ernie.Berkeley.EDU.UUCP (Marc J. Sabatella)
Organization: University of California, Berkeley
Lines: 30
Keywords: unreliable


Having grappled with this problem before, I can tell you several things about
the bloody cursor:

First, setting the start line below the end line has the interesting effect of
creating a two-part cursor (top and bottom) not of turning it off.
Setting both the start and end line to a ridiculous value (only 5 bits are
used, if I remember correctly, so it has to be ridiculous mod 32) works on
some machines, but fails on others (all genuine IBM equipment).  Moving the
cursor off the screen is specifically warned against in several sources, but
seems to work in most cases (certain graphics clone cards used on some brand
name clones don't seem to like it).

An annoying bug in most BIOSes - presumably the cloners decided to clone
IBM's bugs as well - is that the BIOS record of current cursor start line and
end line is *NOT* accurate unless you happen to be in CGA text mode.  In one
application I was writing, I wished to provide a block cursor, and then restore
it to whatever it was before when the program was through, but the BIOS data
area always said the cursor was orignally on lines 6-7 when I went to save it;
even on a monchrome system in which the cursor was actually on lines 11-12
(or somewhere around there).  Looking at the BIOS startup routine listings,
the BIOS data area for the cursor is unconditionally initialized to 6,7.  Turbo
Editor Toolbox (and some TP version) users may already have noticed that the
cursor is an annoying overstrike on monochrome systems, and leaves the cursor
in that state upon exit.  Moral: if you change the cursor shape, be careful
to consider the curren video mode both when setting up the cursor, and when
restoring it (you DO restore it, don't you???).

Marc Sabatella
mjs@ernie.Berkeley.EDU