@bread80@mstdn.social avatar

bread80

@bread80@mstdn.social

Amstrad CPC, RC2014, Z80, Raspberry Pi Pico, TTL processors and the occasional bit of Eurorack

This profile is from a federated server and may be incomplete. Browse more on the original instance.

bread80, to random
@bread80@mstdn.social avatar

With the memory board sent to the fab it's time for the most exciting part of the project: the processor board.

This is A3 sized and houses 117 ICs. I'll be adding as many blinkenlights as I can fit.

I intend to toot as much as I can about the design process. I think it should be ... ahem ... interesting.

But it won't be quick. I'll be fitting it around other projects, and it'll be a ton of work anyway.

bread80,
@bread80@mstdn.social avatar

Here's my top-level schematic for the processor board. I'm starting out by finishing a few things off and a bit of tidying up.

I've just added the labels to link up the connectors on the left with the modules on the main diagram and convert the I/O busses to Kicad busses.

BTW If you're bothered by schematics that don't fit the page size you might want to sit this one out :) Even A3 is proving to small for me here.

bread80,
@bread80@mstdn.social avatar

I did the original 'schematic capture' last year. The images show the first page of originals versus the rough equivalent in my version.

The originals are six pages long but aren't broken down by function. I've moved various parts between modules to make things clearer.

The connectors on the right of the original jump to page 2. They're in the exact same vertical position on both. You could stick the six pages together to read them as one.

image/png

bread80,
@bread80@mstdn.social avatar

If you're interested in the schematics they're in my repository at https://github.com/Bread80/Datapoint2200/tree/main/Processor

There are PNG files included for each of the processor modules. I've made some minor changes since they where uploaded but you'll be able to get the gist of things.

bread80,
@bread80@mstdn.social avatar

Running an electrical rules check but it's choking at a few annotation errors that I'll need to go through and track down :-(

bread80,
@bread80@mstdn.social avatar

Gave myself a scare this morning.

I always picture the with the chips on the memory card facing left as you look at the machine from the front.

But I realised the -12V and -5V pins on the memory cards are on the right end. In that orientation they would at the far end from the edge connectors. Suggesting they were probably mounted the other way around.

This would mean my LEDs on the memory boards were on the wrong edge! And would cause me numerous silkscreen issues. 1/n

Close up of the edge connector on my D2200 memory card.

bread80,
@bread80@mstdn.social avatar

Current status: proof reading the schematics. I’m following every connection and using highlighter pens to mark where I’ve been. And doing the same to my schematics. The assortment of colours helps to stop me getting muddled.

Thus probably counts as tedious but my brain enjoys this kind of task.

bread80,
@bread80@mstdn.social avatar

Adding a page of spare units, based off the table on the original schematics, but the design checker doesn't like it.

So, the original is hard to read, and I've not double checked what I've copied, but it clearly shows Z95 with some spare units. But Z95 is one of the RAM chips making up the stack. So this table is definitely error prone.

The table or spare units from the original schematics. Each entry has fields for unit number, IC type, input pins and output pins. The scanning of some of the entries is poor to the point of being somewhat unreadable.
Kicad rules checker output: Multiple item Z30 (unit 5) Different values for Z53A (7400) and Z53B (7402) Multiple item Z95 (unit 3) Different values for Z95C (7410) and Z95A (7489) Annotation required!

bread80,
@bread80@mstdn.social avatar

Adding footprints. No difficulty here. There's only 8 different footprints across the board: 3 for connectors; 2 for capacitors; 1 for resistors; and 2 for chips.

This was the early days of 74 series logic so only 14- and 16-pin packages in use.

bread80,
@bread80@mstdn.social avatar

Now this is the dictionary definition of tedium. An entire page of power units for the logic gates.

Gaps are for chips with power connections on the main symbol. Not, BTW, the same as chips containing a single unit - there are several 8-input gates with one unit per chip but those still have a separate power unit.

bread80,
@bread80@mstdn.social avatar

I've copied the Decoder PCB to get the edges of the Processor PCB. I'm using a print out of the decoder PCB and the long edge dimension of the decoder board to work out the scale of the print out.

I can then measure and scale up from the print out.

I'll keep the old decoder components and silk screen for the moment to reuse dimensions and design standards.

bread80,
@bread80@mstdn.social avatar

Footprints imported to the PCB designer. Not actually as scary as I was expecting. Let the fun begin...

bread80,
@bread80@mstdn.social avatar

All components placed - to match the positions on the original board. Still some fettling to do on the edge connectors.

I'm now finally realising how ridiculously large this board is. In a way which, for unknown reasons, I'd been completely oblivious to previously.

bread80,
@bread80@mstdn.social avatar

And the rats nest. If that's your thing.

bread80,
@bread80@mstdn.social avatar

@rc2014 @erazmus I’m finding there’s a lot of traces which visit multiple locations in disparate corners of the board. Routing those in a way which avoids forks is proving challenging. I’m used to zooming in and out to plan a route but the size of this takes the zooming to another level.

bread80,
@bread80@mstdn.social avatar

I'm finding the best way to route this is by working through the schematics. The other way, starting with Z1 was challenging due to the length of the traces and the number of destinations.

Doing it this way I can quickly see from the schematic if there's just one or two other pins to visit. That probably sounds long winded but it works form my brain.

bread80,
@bread80@mstdn.social avatar

You'll notice I've rotated the board 180 degrees in the editor.

Routing it this way is helping me to see where functionality lives. Given the natural viewing angle will be from the front (memory cards at the rear) rotating it now saves me having to relearn the map later.

It is, however, a total mind freak to now see everything upside down.

Another benefit to this: the first page of the schematic is the control stuff. So most of the long, winding, traces should now be done.

TheByteAttic, to IT
@TheByteAttic@mastodon.nl avatar

Something is cooking again... This one will come out with a nice golden glaze (no, this is not yet).

bread80,
@bread80@mstdn.social avatar

@TheByteAttic You won’t appreciate this but the Brits will. https://m.youtube.com/watch?v=QrSqXWzB2KU&pp=ygUUQ2hpcCBwYW4gZmlyZSBwc2EgdWs%3D

bread80, to random
@bread80@mstdn.social avatar

It binary digits are called bits then ternary digits must be called ... tits?

rc2014, to random

If you are a jigsaw puzzle aficionado, would turning this photo in to a 1000 piece jigsaw be good, bad or sadistic?

Close up of one area showing a variety of DIP chips, both narrow and wide, with their laser etched part numbers clearly visible.

bread80,
@bread80@mstdn.social avatar

@rc2014 My mum loves a jigsaw. Not sure she’s ready to give up her country cottages for one of these yet.

bread80,
@bread80@mstdn.social avatar

@rc2014 Mine has struck rules. 500 pieces, no difficult areas, and only nostalgic themes allowed.

bread80, to random
@bread80@mstdn.social avatar

Picking up the project. I had to cut the reset line because the picos where being held in reset state.

The board has a small programmable logic chip. One of its functions is to translate the leading edge of the CPCs reset signal into a short pulse. This gives the picos time to boot before the CPC reset ends.

It turns out I had the output polarity wrong. It was giving a short high on the reset line. A quick reprogram and that’s issue 1 sorted 🙂

craiggrannell, to retrogaming
@craiggrannell@mastodon.social avatar

Everyone today: CAPTCHA is evil and getting worse!

Me in 1985: grumbles at Lenslok

The more things change…

bread80,
@bread80@mstdn.social avatar

@craiggrannell I’m just wondering if anyone’s made a phone app that can take a photo and decode it?

haitchfive, to retrocomputing
@haitchfive@mastodon.social avatar

Introducing CERBERUS 2100™, the next step in expandable multi-CPU 8-bit systems, by @TheByteAttic

https://www.youtube.com/watch?v=qViSKIDjwJY&list=PLDf2uklC__d125LRBAzJxqX7rxL6APz4K

[ I really like the multi-processing capabilities, I wonder how hard would it be to create a ZX-BERUS with a handful of Z80s instead of a hybrid dual-headed Z80/6502 chimera. All in all, an excellent project and there's a lot of work that would be reusable to bootstrap anyone who would like to build a SMPeccy. Handy!🙂 ]

bread80,
@bread80@mstdn.social avatar

@TheByteAttic @haitchfive I love the idea of doing a dual Z80 machine. The amount of time it spends in refresh cycles, and the speed of modern memory means you could have two, three, or even four processors all running simultaneously at pretty much full speed.

One day, when the universe gives me a giant pile of free time, I’ll create it 😬

bread80,
@bread80@mstdn.social avatar

@TheByteAttic @haitchfive So far this year I’ve been working to a written list of projects I allow myself to work on. It’s worked very well at keeping me focussed.

But when I review the list I have the option to add new items…

  • All
  • Subscribed
  • Moderated
  • Favorites
  • •
  • JUstTest
  • mdbf
  • ngwrru68w68
  • tester
  • magazineikmin
  • thenastyranch
  • rosin
  • khanakhh
  • InstantRegret
  • Youngstown
  • slotface
  • Durango
  • kavyap
  • DreamBathrooms
  • megavids
  • tacticalgear
  • osvaldo12
  • normalnudes
  • cubers
  • cisconetworking
  • everett
  • GTA5RPClips
  • ethstaker
  • Leos
  • provamag3
  • anitta
  • modclub
  • lostlight
  • All magazines
    •