CDC 6600 display character generation

[Noel Chiappa]

    > From: Toby Thain

    > It's suggested there (without any proof though) that the CDC used a
    > Fourier process
    > ...
    > I'd be very interested to know what you find out about the circuitry.

Someone very kindly pointed me at:

  http://www.bitsavers.org/pdf/cdc/cyber/cyber_70/fieldEngr/60125000C_6602_6603_6622_6681_6682_Data_Channel_Diagrams_Dec65.pdf

(although why it's in the Cyber70 folder, I'm not quite sure :-). I don't
completely understand it (it's only drawings, no text, and the notation is
unfamiliar), but I think I get the general drift - and it's pretty baroque!

Very briefly, it appears to me that characters are generated from short
vector-type strokes placed in a 7x7 matrix, with each stroke being encoded as
motion of 0, 1 or 2 'boxes', both horizontally and vertically, from the 'box'
of the end of the previous stroke. A character can contain up to 22 strokes,
but most seem to average about dozen or so.

The pronounced rounding which I noticed in the characters must be caused by
the limited bandpass of the A-D system, amplifiers, etc - it can't actually do
a sharp corner when going from e.g. a vertical stroke to a diagonal one. Or
something like that.. :-)

	  Noel