Hi Ed,
thanks for the appreciation.

The problem isn't decoding the PLAs, I had translated them to AND/OR gate equivalents.

The problem is understanding in depth what a PLA based state machine does when, how and why.

For instance, the control PLA in an audio channel gives us a 3 Bit state machine.
More than one PLA product term can be active at a time.

Let's just imagine, that two product terms are active at the same time.
One wants the state machine jump to '5', //binary 101
the other wants the state machine jump to '3', //binary 011
the state machine then jumps to '5' AND '3' = '1'. //binary 101 AND 011 = 001

Things like that can give you quite a headache, it's tricky.

;---

Of course there were different 6545/6845 implementations from different vendors, with slightly different features.
We voted for the Rockwell R6545, because it features things like horizontal scrolling and interlaced mode.

Ah, yes, for sure, understanding the state machine is another level!

I have no problem with your choice of R6845 - just noting the variety really, for my own mental picture.

Edit: I see André has a page on differences.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

I'm very glad this work was done - it's possible one could raise this sort of money by crowdsourcing, as there's lots of interest in the precise workings of these kinds of custom chips, and the way to a definitive answer - expensive, labour intensive, and time-consuming though it is - is by way of adventures like these.

I'm also very glad to share the planet with people as interested as I am - maybe a little more interested - in the lowest levels of workings of things, and the preservation of the history.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

BDD, Thanks for dropping by.

Ja, getting maybe 30 chips decapped at 2k€ each ain't cheap. //Meanwhile, the lab has changed the price for a decapping to 2k5€.
But that's just money, money isn't the problem. The problem is time. Time is more valuable than money here.

3 months average for vectorizing a 65xx peripheral chip.
3 months average for extracting schematics from the vectorized picture.

This requires a trained eye and some years of experience, and not everybody can do this.
Frank and me happen to have something like a job and a life...


As somebody had put it:
"68k assembly coding is like to walz.
After RISC or x86 assembly coding, you feel like crawling out of the boxing ring, trying to remember how and when you got the one or other bruise."

My impression is, that the Amiga designers were quite good, and they sure knew what they were doing and why.
But the management at Commodore never had sort of a clue what it got with the Amiga, and what do do with it.
//Just let me mention the NewTek Video Toaster and "Babylon 5 space scenes"...
//...now: why didn't Commodore invent something like the Video Toaster ?

BDD and Ed:
Trying to imagine how much cool technology went dumped into '/dev/null' over the past 50 years
because of incompetent managament, bad product\price politics, dogma and such sure gives you odd numbers...

We are just trying to preserve some of it. //At some point in the future, all of the original chips might be gone.

;---

Of course Frank and me have taken a look at the VDC datasheets,
and from the VDC register map it's obvious that the chip _has_ to be built around a 6845\6545.

But it will take some time until we can pay attention to the VDC.
TED and VIC-II have to be done first.
EF9367 also is interesting: there had been fast vector graphics for the PET.