Sigma Electronics Systems Display Generator 5564
paulkoning at comcast.net
Fri Mar 6 12:33:26 CST 2015
> On Mar 6, 2015, at 1:07 AM, tony duell <ard at p850ug1.demon.co.uk> wrote:
>> One of the full-width cards is something like 'area fill'. So it does that in hardware too?
>> Yes, probably, it is not that big trick (in theory). Example Amiga's custom chipsets was capable for area fill (line
>> mode), and btw, prototype of that custom chip set was made from TTL chips:http://www.floodgap.com/retrobits
> Sure. My guess is that the line drawing on this terminal is going to be similar to that on the HP2623. A simple
> state machine where the main CPU (in the HP a Z80, in the Sigma a 6800) calculates various parameters and
> the state machine goes along setting pixels. The area fill board is perhaps 50 or so TTL ICs. Not complex
> really. But I think it is a high-end feature for a 1970s terminal.
It’s interesting to compare with the PLATO terminals. The first plasma panel terminal (“PLATO IV”, “Magnavox”) is from the early 1970, all hardwired logic. It does line drawing in hardware, essentially the Bresenham algorithm. It doesn’t have area fill.
The “PLATO V” terminal is a 1976 successor, using an 8080 with some hardware assist (the Bresenham per-pixel step is in hardware, but the full line loop is in software). That one initially did not have area fill but a somewhat later successor added that, in software.
So, high end feature, I suppose; PLATO terminals were used in fair numbers but were not mainstream graphics terminals.
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