17 Jul
2001
17 Jul
'01
9:02 p.m.
see inline comments below, plz.
Dick
----- Original Message -----
From: "Pete Turnbull" <pete(a)dunnington.u-net.com>
To: <classiccmp(a)classiccmp.org>
Sent: Tuesday, July 17, 2001 5:36 PM
Subject: Re: Light Pens ...
On Jul 17, 16:54, Richard Erlacher wrote:
If you have multiple colors, you will have to have multiple shift registers, and
a character, normally based on the shift-register width used with characters, is
typically 8 bits. That means 8 bits per color. I suppose it's possible to use
fewer dots per character, but that means slowing down the pixel rate, since the
6845 can count only so fast. I think 500 nS per character, implying 8 bit
character width, in each color, is the max, though I'm running on very much aged
memory. The high-speed timing logic, external to the 6845 is what resolves the
individual pixels to a character block.
Viewed from the 6845, is the block 1 scan line
high?
Yes.
Getting the horizontal location right, as
you'd have to in order to do
precise
drawing, might be a bit more complicated,
don't you think? an 8-pixel
extent of
uncertainty is quite a bit on a 640-pixel
display.
But it's usually less than 8 bits. For example, the pen I built (which had
assorted other problems as per my other responses) was mostly used on a
4-bit-per-pixel display (16 colours) or a 2bpp (4 colour) display, so the
resolution was usually 2 pixels or, at worst, 4.
--
Pete Peter Turnbull
Network Manager
University of York