19 Oct
2008
19 Oct
'08
11:25 a.m.
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
character.
-tony