robert@gitpyr.UUCP (Robert Viduya) (04/02/85)
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I'm currently writing a terminal program for the PC and one of the cap-
abilities I'm building into it is the ability to change your cursor.
I want to support block-cursor, blink-block-cursor, underline-cursor
blink-underline-cursor and an invisible cursor. I've got everything
almost done, with the non-blinking cursors done via character attributes
and the blinking cursors done using the real cursor. However, I'm
running into a major difficulty making the real cursor disappear
whenever I switch to a pseudo-cursor (non-blinking) or an invisible
cursor.
I know you can make the cursor disappear by moving it off the end of
the screen, but I'm using the hardware scrolling capabilities of the
6845 CRT Controller (as opposed to moving blocks of memory around as
IBM chose to (yuck :-)) and the end of the screen changes everytime
I scroll up or down a line. I could keep up with where the end of the
screen is, but I'd rather not. Since I want this thing to operate
at 9600 or greater baud, I want it to be as fast as possible (it
actually talks at 19200 baud right now, with XON/XOFF handshaking,
but screen I/O slows it down so that there doesn't appear to be
a difference between 9600 and 19200).
I tried using the following to turn the cursor off (in C):
outp (0x3B4,10); /* select cursor scan-line start */
outp (0x3B5,0x0E); /* one greater than max scan line */
outp (0x3B4,11); /* select cursor scan-line end */
outp (0x3B5,0x0E); /* again, one greater */
Since the maximum scan line address is 0x0D, setting the cursor to
one greater than that should turn it off. This worked MOST of the
time. Every once in a while, I would get a blinking block cursor,
however. It isn't very consistent, so I have nothing to go on except
for the possibility that it might be a timing problem (which I hope
it isn't).
If it makes any difference, I'm using the monochrome adapter. I've
got the code in to handle the color-graphics adapter (really, just
changing the port addresses), but I haven't had the chance to test
that out yet.
Can anyone give any hints on this? Thanks in advance.
robert
--
Robert Viduya
Georgia Institute of Technology
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