Sigma Electronics Systems Display Generator 5564

tony duell ard at
Mon Mar 9 16:04:28 CDT 2015

> Thanks for photos!
> Chip codes seems from 77...79.  It is obvious, it is not mass producted (board type, also serial no. of vector 
> board is 039). Maybe tailor made for some special CAD system?

The fact that 2 of the boards are wire-wrapped not PCBs suggests it was a low-production unit, but equally it 
is too well made to be a one-off kludge IMHO.

> "Vector Gen" board seems some nice Signetics chips, like weird multiport 8x4-bit ram (82S112), maybe used as 
> some buffer? Top of that same card goes 12-bit bus to 8263 multiplexers (wild guess: 4-bit for each color?).  

I suspect it's similar to the little state machine in the HP2623 terminal for line drawing and these RAMs contain the
parameters for the state machine.

I doubt it's 4 bits per colour, I suspect lines are drawn one at a time, you specify the colour, the state machine
does its thing and the colour setting simply determines which bits in the video RAM are changed. So the 
vector generator would not know anything about the colour

> Also there is  32x8 PROMs (82S23), maybe used as glue logic / sequencer, too small for look up table.

I think that's a state machine type of sequencer.

> How many 16Kx16 + ALUs board there were? Three? Maybe there is one processor/memory for each color 
> plane...

6 of them. It might be 2 boards per colour, but one thing I didn't notice until later were the 74189 RAMs on
the video processor board (the one with the DACs on it). My guess is that these are a colour look up table
forming a mapping between bits in video RAM and the DACs (maybe 3 off 5 bit DACs). This suggests 4 bits
per pixel (to address the CLUT RAMs) at the video memory side, how that fits in with the 6 Pixel Store boards
I don't know. 

> You have to put that back to live, and make some reverse engineering. It seems to be really exciting machine!

It is going to be a big job to sort it out, but one that will be worth doing. That is, unless manuals for it turn up...


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