Search found 548 matches

by guesser
Sun Aug 30, 2020 11:30 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

This has been my feeling since we saw the first die shot and it was clearly not just a mask programmed micro like the couple of chips someone pointed out that explicitly say so in their datasheets, just holding on to the possibility that it was cobbled together out of some existing blocks from somet...
by guesser
Sun Aug 30, 2020 12:06 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

In case anyone needs something different to look at over their morning coffee, here's a 1772 die shot. https://siliconpr0n.org/map/wdc/wd1772/mz_mit20x/ Is it me or does it look a lot simpler? Are we going to have a race then? Team B's chip looks simpler, but team A have had a week head start :lol:
by guesser
Sat Aug 29, 2020 11:05 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

I've not really studied that structure at all to see how the rows and columns are selected, it's not got an obvious address decoder like what we're calling the ROM. Both halves of it have a ton of empty space too which is a bit perplexing.
by guesser
Sat Aug 29, 2020 9:47 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

This is because I decided to go tracing those "extra two" bus lines -- bits 8 and 9 -- which the Seventh-Day True Microcontroller Believers are calling the page bits. I have this so far (in blue-green). The blown-up region I posted is the eastern end of one page line, which is presumably ...
by guesser
Sat Aug 29, 2020 9:38 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Diminished wrote:
Sat Aug 29, 2020 9:04 pm
Here are the exported SVGs of bits 8 and 9. I'm working at 50% (133 MP) instead of 100% now, so you'll have to scale them accordingly.

page_paths.zip


Viel Spaß!
Ta, that's those added to my file, for anyone else playing along at home :)
by guesser
Sat Aug 29, 2020 9:09 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Diminished wrote:
Sat Aug 29, 2020 8:54 pm
Ah yes, it's obvious now I look at it again. I've been staring at this too long. :shock:
I've been hooked completely by this (as you can probably tell by the timestamps on my posts) and a couple of times this week I've seen polysilicon wires when I close my eyes :shock:

:lol:
by guesser
Sat Aug 29, 2020 8:42 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

BigEd wrote:
Sat Aug 29, 2020 8:18 pm
That's really weird - whereabouts are we? And can we see more context please? (maybe 3x)
Immediately to the right of the ROM output tap on the "green" bus line.
by guesser
Sat Aug 29, 2020 8:40 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Anyone have any objections to seeing if I can reach a bored retro chip expert via Twitter (with links to some of the resources on this thread)? Not if it's Master Ken, I'd be embarrassed thinking he's reading my bumbling amateur analysis! :wink: (That and he'd have the whole thing reversed in an ev...
by guesser
Sat Aug 29, 2020 8:36 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

That's a metal to diffusion via with a couple of gates around it like the connections to the bus from the output of the ROM I finished tracing out last night.

e.g.
bus-output.png
The diffusion silicon is presumably connected off to gnd somewhere off the image is it? EDIT: ah yes, found it now
by guesser
Sat Aug 29, 2020 8:00 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Also the address decoder is plainly a straight binary count even if the lines were scrambled up, which they don't appear to be.
by guesser
Fri Aug 28, 2020 11:05 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Diminished wrote:
Fri Aug 28, 2020 8:46 pm
here's one interesting thing
I've noticed a couple of odd bits of metal going nowhere, but none as long as that!
by guesser
Fri Aug 28, 2020 8:03 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

1024MAK wrote:
Fri Aug 28, 2020 8:00 pm
Think valve with the grid at a voltage that only just biases the valve on...
Oh heck, don't ask me to learn how valves work too... :lol:
by guesser
Fri Aug 28, 2020 7:38 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Got it, thanks :)

Once you know, it seems so obvious heh.
by guesser
Fri Aug 28, 2020 7:18 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

Yep, those would be typical pullup structures: a very weak transistor with the output connected to the input. (Also it will usually be a depletion mode device, which means it tends always to be on, but that's not usually important: a weak transistor wired as a two-terminal device here acts as a res...
by guesser
Fri Aug 28, 2020 7:16 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller de-cap and craziness -- do not try this at home!

How have you tried to determine the ordering of the address lines and data lines from the ROM? I've not really got any further there because I'm trying to understand the circuits as I go along rather than branching off on too many fronts at once. Analysing that scary mess above the bus is a bit muc...
by guesser
Fri Aug 28, 2020 4:37 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

I'm still not really sure about the two big polysilicon things, I can't really tell clearly what they're connected to. I'm working on the principle that there's a connection from the diffusion silicon to the polysilicon at the ends away from the positive rail, but I still don't know enough about the...
by guesser
Fri Aug 28, 2020 12:47 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Here's my attempt at the whole ROM circuit. rom-circuit.png The box surrounds the circuitry in my previous image, plus the transistors onto the bus. I added the pull down resistor in the bottom right to stop the column floating at half the supply voltage in my simulator, this represents the leakage ...
by guesser
Fri Aug 28, 2020 3:58 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Here's where the bits go before they get onto the bus. The polysilicon disappearing off the top looks to form a transistor for pulling the bus line down to ground. The polysilicon coming in from the right, and the piece it passes next to both connect up to the metal layer and are common inputs for a...
by guesser
Fri Aug 28, 2020 2:22 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

The "Active layer" diagram looks like our ROM.

The columns are pulled up to Vcc at the bottom. The decoder is implemented the same way but rotated 90° and with two input lines to each "bit".
by guesser
Fri Aug 28, 2020 12:33 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

The part shown is just the first three bits worth, each group of 8 columns is one bit.

I've uploaded the full res image of the whole ROM here: https://temp.zxnet.co.uk/8271/rom.jpg

Feel free to point out any transcription errors I missed :lol:
by guesser
Fri Aug 28, 2020 12:15 am
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Ahh, that's great! Not sure which photo that is, but you're seeing much more detail there than we were in the original photo; the subtlety of how those things are connected to each rail was totally lost before. Are you confident about the address decoding yet - can we have another go at putting tog...
by guesser
Thu Aug 27, 2020 11:23 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

The ROM is constructed like this rom.jpg Note those annotations are what I transcribed originally, which could be inverted base on those possible 8048 instructions. We're assuming the top three rows are the column address decoding, for each combination of bits all the columns within each bit will be...
by guesser
Thu Aug 27, 2020 11:09 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Rich Talbot-Watkins wrote:
Thu Aug 27, 2020 10:02 pm
OMG! Seems like we might really need to get a good handle on how this is all connected up before attempting to even form bytes, let alone disassemble.
Yeah, I think this is wise.
by guesser
Thu Aug 27, 2020 6:58 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

I want to try to find my way from the bond pads back to the bus as that should fix the bit ordering.
by guesser
Thu Aug 27, 2020 4:55 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

I've started converting the bus lines to polygons and separating them into the different layers. Only done "white" so far as I spent an hour reading about diffusion regions and polysilicon. Not sure whether to go through all the stuff Diminished already traced out first, or follow the sign...
by guesser
Thu Aug 27, 2020 3:28 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Diminished wrote:
Thu Aug 27, 2020 3:16 pm
I suggested the bus was 8-bit, and that it was the internal bus, i.e. the one that is clearly mentioned on the data sheet.
Oops, so you did sorry. There's two extra signals and sets of taps running along that centre section, I'm not sure how far they follow the others.
by guesser
Thu Aug 27, 2020 2:52 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

I would expect to see 32 bytes of RAM (or 8-bit registers) which correspond to special registers 0-31. These may or may not include a program counter. I'm pretty sure the RAM is in the bottom right. There could be 32 bytes there, with some of them being special purpose in some way. i.e. more than j...
by guesser
Thu Aug 27, 2020 2:27 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

There's yet more ROM structure in the middle, directly below the big ground metal branch.
by guesser
Thu Aug 27, 2020 2:25 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

There's another huge ROM-like structure in the top right, which I suppose I had better dig into and see if I can work out what it is. How are we expecting instruction decode to work? Each instruction being a sequence of rows in a ROM and the output of that is further decoded by some combinational l...
by guesser
Thu Aug 27, 2020 2:09 pm
Forum: 8-bit acorn hardware
Topic: 8271 disc controller de-cap and craziness -- do not try this at home!
Replies: 449
Views: 23507

Re: 8271 disc controller craziness -- do not try this at home!

Diminished wrote:
Thu Aug 27, 2020 1:23 pm
What if the address decoder ROM bits are inverted, too?

You could have weird arrangements where bits 0-2 count upwards, but bits 3-7 count downwards ...
Having them all inverted would make the addresses run from $014 - $3FF instead of $000 - $3EB.

Go to advanced search