CRT displays [was: computer graphics in the 1950s]
ard at p850ug1.demon.co.uk
Sun Oct 19 13:25:49 CDT 2008
> The Datapoint 2200 used a serial mos memory in its first incarnation.
> Sweeping each row of text implies scanning the same characters seven
> times in a row. They couldn't afford to add a line buffer, so they
> invented "diddle scan".
> They actually scan to the upper left corner of each character, then
> sweep out the 5x7 dot matrix for that character, before adjusting the
> x,y deflection to the upper left corner of the next character.
I seem to recall the DEC VT11 (and thus GT40) did something similar. When
it displayed a character it scanned a little raster at the appropriate
place on the screen and used a normal dot-matrix character generator to
turn the beam on and off.
The HP1350, though, had a set of ROMs that were tables of the vector
movements needed for each character. It didn't scan a raster for each
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