@bread80@mstdn.social avatar

bread80

@bread80@mstdn.social

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

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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!

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 #amstrad #picogarry 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…

rc2014, to random

This isn't a mutant alien Pacman ghost. It's a custom tool I made a few years ago, and has been invaluable in preparing the Pride kits.

I should probably write a short blog post about it. In the meantime, see if you can work out what it's used for.

(I have only ever needed it for the RC2014 Mini After Dark and the Pride kits)

bread80,
@bread80@mstdn.social avatar

@rc2014 I’ll hazard a guess it’s for bending pin headers. If, say, they’re not available in the required colour. But I’m not sure the plastic would be strong enough for that use case.

mos_8502, to random

Okay, just need to put in a couple of holes for cable ties, to fix the cable to the Pi Pico, and figure out what, if any, other wiring the Pi Pico needs.

bread80,
@bread80@mstdn.social avatar

@mos_8502 Are you sure there’s enough height under the Pico to attach a USB cable (if the Pico is surface mounted)? I’ve always mounted them with the USB at board edge to be sure.

kelpana, to random

Hello Mastodon, please encourage me to finish my @rc2014! I have not been feeling great lately and just have been rather down in the dumps with lack of work. I need to do something to encourage myself.

bread80,
@bread80@mstdn.social avatar

@kianryan @kelpana @rc2014 I notice most people do the one-module-at-a-time thing. I built mine by component. All resistors of value x, then all of value y etc.

For me it felt more reassuring. More confidence I hadn’t put a value in the wrong place. Knowing that I would have left over parts, or shortages when I got to the end.

rc2014, to random

I was Today days old when I discovered that you could attach an email to another email in Gmail.

It's actually really easy and intuitive. I'd just never found a way to do it before.

bread80,
@bread80@mstdn.social avatar

@rc2014 It’s emails all the way down.

amoroso, to random
@amoroso@fosstodon.org avatar

YouTube is going to serve way more ads, so it's a good time to remind books have no ads.

bread80,
@bread80@mstdn.social avatar

@amoroso I notice Amazon Prime ad supported stuff is two or three ads max in a thirty minute show. Given YouTube only pays creators a pittance I fail to see any justification for the quantity of ads beyond greed.

rc2014, to random

Breaking News: my DHL driver hates me

Possibly Related News: over 30KG of PCBs and 6KG of ICs have just been delivered.

bread80,
@bread80@mstdn.social avatar

@rc2014 Is this a warning call for us to pay down the credit cards in readiness?

bread80, to random
@bread80@mstdn.social avatar

There are some clever multiply routines out there. But for my money the one takes the prize.

It starts by testing if both operands are < 255. If so the result must overflow, so it aborts.

It then short cuts if either operand is zero.

It also short cuts if the multiplier is one or two (if only tests one operand though).

So the final loop is a 16*8 multiply. And even then it skips any leading zero bits.

;At this point, first operand is in HL and DE, second in A cp $03 ;Is multiplier one or two? Is we can short circuit jr c,.one_or_two scf ;Shift a 1 into bit 0. This is our 'stop marker' .find_first: adc a,a ;Left shift to find the first bit. Note that we know A is non-zero jr nc,.find_first .mult_loop: add hl,hl ;Left shift the result ret c ;Overflow add a,a ;Next bit to CF jr nc,.skip_bit add hl,de ret c ;Overflow .skip_bit: cp $80 ;Finish when the 'stop marker' hits bit 7 (other bits will be zero) jr nz,.mult_loop ret .one_or_two: ;Multiply by one or two cp $01 ret z ;Mutliply by 1 add hl,hl ;Multiply by two ret

rc2014, to random

The red LED was a huge breakthrough, which I think we all agree on. And the blue LED was a massive game changer, resulting in a Nobel prize. Even if blue LEDs are overused these days, they were key in paving the way for the white LED.

The next big thing will surely be the brown LED. Once scientists have cracked that, then we're well on our way to the black LED. So, come on scientists, stop resting on your laurels, and get on with brown LED development! Stat!

bread80,
@bread80@mstdn.social avatar

@rc2014 I’m always disappointed at the limited colour range available: red, orange, yellow, green, blue.

The human eye can see 24 million colours (or something like that). So where are all the other colour LEDs? Why can I not design electronics with a pastel vibe? Or any other colour space without having to resort to RGB LEDs.

Raspberry_Pi, to random
@Raspberry_Pi@raspberrypi.social avatar

this is apparently an "octothorp".

What.

bread80,
@bread80@mstdn.social avatar

@Raspberry_Pi So we should all be saying “octothorpetag”?

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