CDC 6600 display character generation

[Toby Thain]

On 2018-06-06 12:31 PM, Noel Chiappa via cctalk wrote:
>     > 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.

OK, so that's definitely not a Fourier technique.

I admit I was sceptical of the tweet. :)

Thanks for the link.

> 
> 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.. :-)

Makes sense.

--Toby

> 
> 	  Noel
>