18 Oct
2008
18 Oct
'08
2:23 p.m.
On Fri, 17 Oct 2008, Tony Duell wrote:
I once worked on some kind of scientific instrument, controlled by a NOVA
1210 IIRC which displayed a graph on a 9" composite video monitor _turned
on its side_. This considerably simplified the circuity -- all the vidoeo
circuit had to do was generate sync pulses and then turn on the video
signal for a short time (giving a 'pixel') at the right time after each
line sync pulse (thus putting said 'pixel' at the right height on the
screen).
Actually, I believe there was a CRT-like device
(I forget the name --
'Charactertron'?) where you did sort-of send the characters to the CRT.
THe CRT had 3 deflection systems and an electode between them that
cotnained the patterns for all the xymbols (characters, etc) that the
device could display. You used the rearmost deflection system to direct
the beam from the electron gun at the right pattern and the front
deflection system to put it at the right place on the screen. No, I don;t
have one.
Interesting.
This reminds me of the CRT display of a Cogar C4 (or ICL/Friden 1501). It
is a standard 5" CRT with an almost ordinary deflection system. But the deflection itself is rotated/mirrored, i.e. the
"vertical" sweep is from
left to right and the "horizontal sweep" from top to bottom. So the
display controller writes all characters from the first text column first
(and then IIRC only the text lines 1,3,5 and 7). Then comes the next
columns. After all 32 columns come the even text lines (there's a display
mode which only displays lines 1,2,3 and 4; the display has a 32 x 8
character cells). But that's not all. There is a second horizontal
deflection coil that interferes with the first main deflection coil (I
think this is called twiggle sweep or something like that). This second
coil deflects the beam according to the width of one character cell, and
one raster line of a character is written on the screen during this time.
That sounds a bit like the display circuit for the HP9100 calculator.
This machine displays 3 rows of '7 segment' digits on an
electrostatically-deflected CRT. There are, IIRC, 2 integrator circuits
for each axis, the outputs are combined and fed to the deflection plates.
One integratro for each axis is used to geenrate the individual segment
lines, the other is used to move between characters or rows.
The Charactron, though has 2 entirely separate deflection systems
operating on the beam at differnt points. As I understand it, there's an
electron gun, a deflection system to get the beam at the right point on
the 'character generator target', then a second deflection system to get
that character image at the right place on the screen.
-tony