@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
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I’m reading up on this XZ security issue. Does it affect the XZ80 and XZ81 or is it only the XZ Spectrum that’s at risk?

bread80, to random
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Everyone: Amstrad is back!

Me: That kerning is atrocious.

bread80, to random
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Say hello to the CPC Modular. This is an built using a slightly modified backplane. Not exactly an RC2014 due to Amstrad IO quirks.

Current status: video is outputting at correct frequencies but SCART converter isn’t detecting a proper signal. But that means CPU and ROM are working and configuring the 6845.

The design uses SRAM and modifies a few signals in order to do that. Im suspecting an issue in those circuits.

Front view.
Front three quarters view.

bread80, to random
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Returning to the Z80 ALU core implemented in relays. The first task is to redo the relay symbols. Kicads default generic relay shows the solenoid repelling the contacts, rather than attracting them. It's messing with my head.

In the image I've update the two symbols on the left. The rest are still defaults.

(PS Kicad only has a generic symbol for the single pole relay. I extended this to create the tow and three pole versions).

#RelayLogic

bread80, to random
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I'm adding a basic terminal to the 2200 simulator. It's listening to output ports (input still to do).

Here's a video of it saying "Hello World" in it's own fashion. Program listing in video comments.

https://youtu.be/FzSDf94Q0Ao

bread80, to random
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How’s your Sunday morning going? I’m playing Buckaroo with oscilloscope probes.

If you’ve never used these you have now idea how easily they spring off.

bread80, (edited ) to random
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What is your preferred choice of backplane connector for a modular 8-bit computer?

Do you have a preference on price, useability, durability, ease of module design?

Is there any difference from an electrical perspective (signal integrity)?

I'm thinking of maximum signal frequencies below 20MHz.

Boosts appreciated.

bread80, to random
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I've not come across this project before. A modular Commodore 64. Link (in German): https://www.forum64.de/index.php?thread/108496-tube64/&pageNo=10

bread80, to random
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If Gulliver’s Travels was written today it would be about the GIFfians and the GIFfians, who fight wars over pronunciation.

Also, the book would be pronounced Julliver’s Travels.

bread80, to random
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I'm back onto the this weekend. This time working on the cards. I've tweaked the connectors for consistent placement in both X and Y dimension and finished the outline for the lower half of the boards - ventilation slots at the top still to be finalised.

I'm now redoing the traces to/from the connectors - here you can see the connector had to be nudged to the left so the traces aren't quite aligned properly.

bread80, to random
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Not much progress on the this weekend. I've been procrastinating about finalising the vents[0] along the top. Lots of finicky dimensions to measure and calculate. But the first PCB now has a completed outline and I now know how to bend KiCad to my will.

Hopefully a bit of tactical cut and paste will apply this to the other boards.

[0] Anyone claiming these aren't vents risks getting slapped in the face with a ZX80.

The same board in the KiCad layout designer. Looking surprising neat, if I do say so myself.

bread80, to random
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Next up for the is a CPU board. The original version for RC2014 used a standard RC2014 board, but I need one with an MX4 connector.

Not the most complex schematic to design, and the PCB will be pretty barren. I've added LEDs for the I/O address lines. Potentially they'll show which devices are being accessed. More usefully they'll show if the CPU is running, something I would have found very useful on previous computer builds :)

bread80, to random
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I was aiming to get the to the fab before Christmas, but I've been distracted by other projects the last week or two.

But the keyboard is now fully updated:

  • Connectors changed to IDC headers for convenience.
  • New connector added for the Modular, using a '6128 pinout. At the back of the PCB for better cable routing.
  • Larger legend which may make it practical to use cheaper switches.
  • Locating lugs added to switch footprints for easier assembly.
bread80, to random
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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 🙂

bread80, to random
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RIP Z80 🥲

End of life notification letter:
https://www.mouser.com/PCN/Littelfuse_PCN_Z84C00.pdf

bread80, to random
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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

bread80, to random
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BBC micro people: our BASIC has a built in assembler.
Amstrad people: we see your built in assembler and raise you MAXAM.

Dtl, to random
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Looking at the has anyone wired up the GPIO and done bit banged video from that rather than use the built in video stuff?

bread80,
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@Dtl Compared to a Pico it’s only single core and a much slower clock speed. I’m guessing it’s doable but with low resolution and frame rate.

bread80, to random
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And I only just found this. I didn’t realise the Flan name actually made it into production.

This means it’s a revision 4 board, from the first production run. The run with bugs in the video chip and ROM.

bread80,
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@saustrup Just something I read on the Enterprise Forever forum. The issue 4 had the Flan name on the board. Those were the boards used in the Enterprise 64s. I don’t know anything beyond that. I got the impression that was the first production run. Presumably the earlier issues were prototypes.

bread80, to random
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After an evening wrestling with Inkscape I’m ready for an early night. But the diagram actually looks pretty good, and means I’m significantly closer to publishing an article I wrote six months ago.

bread80, to random
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I’m secretly happy about the Sonos app-pocalyse. It’s given me the kick I needed to finally ditch it and move to something (hopefully) better.

bread80,
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I’m moving to Denon HEOS. I’m hoping that something from an established audio company with a long history - rather than a tech industry start up - will mean a slower path to enshittification.

bread80,
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@RetroFunPL New ‘improved’ app, rewritten from the ground up.

The UX is horrible. The key pain point for me is that there doesn’t seem to be any way to connect to the NAS. Although it did work for the first five minutes, but the artists list had no A-Z quick links and I was having to scroll down through several hundred entries.

bread80,
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@RetroFunPL zone day I’ll have cable everywhere and LAN sockets. Not sure I want the hassle and disruption just yet though.

bread80, to random
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AI in science fiction: Insufficent data, unable to compute.

AI in the real world: Here’s a couple of pages that sound plausible.

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