CDC 6600 display character generation

[Toby Thain]

On 2018-06-06 9:48 AM, Noel Chiappa via cctalk wrote:
> Hi, I'm hoping someone here knows the low-level nitty-gritty on how the
> characters on the CDC 6600 console CRTs were generated.
> 
> Thornton, "Design of a Computer", says "Control of the beam .. is provided by
> electrostatic deflection ... electronically converting from the symbol .. to
> deflection voltages", but alas, doesn't say how that conversion is done. And I
> looked in some CDC 6600 documentation online, alas, even less detail.
> 
> But looking at the characters (reproduced on the dust jacket), the curves sure
> make it look like it wasn't anything simple (e.g. using display vectors, as
> one source indicated). Does anyone know?

Ah, this is a topic of great interest to me, and coincidentally it came
up recently on Twitter.

https://twitter.com/TubeTimeUS/status/1003752120867123200

It's suggested there (without any proof though) that the CDC used a
Fourier process similar to the 1958 article by Kenneth E. Perry and
Everett J. Aho (MIT Lincoln Labs).

http://www.thecorememory.com/GenCharforCRR.pdf

A more modern implementation is here:
http://www.glensstuff.com/fouriersynthchargen/fouriersynthchargen.htm

This is actually something I intend to build myself with a larger
character set, and I've been specifically considering emulating the
character set of the CDC console.

I'd be very interested to know what you find out about the circuitry.
Anyway the LCM seems to be the bunch who knows most about it, and
they've seen this thread. I hope the discussion will continue in public.

Related: I'd very much like to get good macrophotography of the console
character set.

> 
> (BTW, the VT11 in DEC's GT40 used bit maps for its built-in character geneator,
> and the hardware did tiny raster zones to display them!)

As does the PDP-1 (point plotting, 5x7 I think).

--Toby


> 
> 	Noel
>