Retro CPU tinker boards/kits?

[paulca]

I want a retro-CPU 'pet'.  Basic bare bones CPU with minimal IO, aka, no display, just tty/uart/i2c IO.... maybe a Wifi "ROM sim" ala ESP32 later on (ie, you can flash it's ROM over the air).

I have considered breadboarding it baremetal, datasheets only.  However, strawmaning the effort and cost steered me more towards something that has already passed the "Breadboard" phase and maybe comes as a basic modular kit?  Even if it's just OSH gerber packs.

So I don't mind a dozen little PCBs with ribbons everywhere stuck to a 30cm square wooden board.

At the same time I don't want to buy a modern Amiga or Spectrum clone fully built with an arduino in it, which believe exists.

Something in the middle.  Like a PCB with the main CPU, a PCB with RAM, a PCB with (EP)ROM, a PCB with the peripheral IC and basic IO interfaces.  etc. etc.  PSU, Clock... the list goes on.

The CPUs I had in mind were the Z80 and 68000.  Two CPUs which I have done an ASM tutorial in at some point when I was a kid.

Can anyone make any recommendations while I go trawling myself?

[brucehoult]

https://www.olimex.com/Products/Retro-Computers/

?

Many of their products are stocked at Mouser and/or Digikey.

[neillnz]

There is this thing:

https://zeal8bit.com/

[paulca]

Thanks.

ChatGPT did googling for me and figures this is what I'm after:
https://www.mega-micros.co.uk/

The downside is... its "Email the guy for quote" ordering affair.

[paulca]

There is this thing:

https://zeal8bit.com/

Yea, what I am finding a lot of are SBCs.  SBCs which are basically modern day SBCs that someone built around a Z80 or 68000.  They are tiny, probably using 6 layer boards and come with every single bell and whistle crammed into it on mostly surface mount micro-circuitry. 

While cool.  I'd buy it, get about 2 hours of fun from it and it will collect dust.  I can probably get more fun out of the UAE emulator with all the settings janked that those SBCs.

I kinda want something more basic.   More spread out.  Modular.  Maybe get a few dozens of hours fun before it goes to the project bucket.

Basically just one step up from a "Ben Eater breadboard" version.

[johnboxall]

https://www.tindie.com/products/tec1/tec-1g-z80-single-board-computer-kit/

[DLJ]

How about an arm 7?
I am fond of the "Atmel AT91EB40 Evaluation Board". This board was the featured board used in the book "Embedded System Design
on a Shoestring" by Lewin A.R.W. Edwards (PDFs are are available)
Atmel ( Now part of microchip) also provide a user guide.
So plenty of documentation and examples, and fairly retro.

I have one available if you are interested. ( postage cost only)

Regards
David

[themadhippy]

I want a retro-CPU 'pet'.

wouldnt that be a 6502, whilst breadboard theres https://eater.net/6502

[Doctorandus_P]

There are quite a lot of such projects on the internet, both for Z80 and 68000 and others probably too. And the state of those projects vary from youtube video's with little extra info, to complete PCB projects (several in KiCad), and to complete kits. Some of the Kits also have (KiCad) schematics and PCB design files available, both easier for you, and by buying the kit you give a thumbs up to the original creator.

Just one example is:
https://hackaday.io/project/164305-roscom68k/

But it's not my thing, I rather buy a EUR 3 microcontroller with 10x the speed of these old things.

A very long time ago I nearly bought a stack of network interfaces for (even then) old HP printers. It was a PCB of about 120 by 120mm, with an 68000, ROM, RAM, Ethernet and I/O to plug directly into a laser printer.

[MarkL]

Here's a modular Z80 system with a mini-backplane, reminiscent of the old S100 systems, and lots of interface (card) choices:

  https://rc2014.co.uk/

You can buy the kits here:

  https://z80kits.com/

Another interesting add-on: If you have an old HP/Agilent logic analyzer, someone developed a probe card for this bus, which can be used for program tracing/debugging:

  https://github.com/MustBeArt/LAIR


I haven't pulled the trigger to get one of these RC2014 systems, but it's on my list when I have some time.

[Doctorandus_P]

Also noteworthy: The original BBC Micro, with only some small modifications done by MikesElectricStuff...

[pqass]

After building a breadboard 8085+UART+PPI the enthusiasm wore off quickly after writting a few hundred lines of assembly. 
I wanted to stretch out with a bigger machine but still be breadboard friendly and found the 68008 (fits on 2 strips, 11 DIP packages: OSC,555*2,68008,'138,'00,'32,'20,62256,29F010,16550).
It's very easy to program in C with the occasional assembly (tools used: binutils-m68k-linux-gnu.x86_64 and gcc-m68k-linux-gnu.x86_64).
I've adapted the monitor from the Gloworm OS project (see under src/monitor/).
I also found Bare Metal m68k very useful as I come from an application programmer background (I didn't know what happened before main() was called).
The Computie68k project (in several revisions from 68000 to 68030 with 2MB SRAM, 512KB Flash, 68681 DUART) is documented in Kicad with board layouts.
Also, check out the Gloworm OS. It's a basic UNIX-like OS recreation.

[pcprogrammer]

How about the MiSTer FPGA. https://en.wikipedia.org/wiki/MiSTer It is an open source FPGA project that allows one to setup almost any old retro system with the CPU configured in the FPGA. No emulation, but a cycle accurate copy of the original chip for a lot of them.

It can be setup as a game console or a microcomputer, so good for many hours of play time. Both the Z80 and the 68000 are available in the form of for instance the TRS-80 or the Atari ST.

Expansion boards and other stuff can be bought here: https://misterfpga.co.uk/ or here https://misteraddons.com/ or here https://ultimatemister.com/

Not cheap, but very flexible.

[SiliconWizard]

Tindie has a number of these kits, you also have modular Z180-based kits, such as this one: https://www.tindie.com/products/tindiescx/sc792-z180-romwbw-cpm-computer-kit-for-rcbus-80/

Pretty cool if you were familiar with the Z80 but want to take advantage of this retro phase to try something different. The Z180 was relatively uncommon, and while mostly compatible with the Z80, adds many nice features we wish we had back when we were using Z80 computers!

[brucehoult]

But it's not my thing, I rather buy a EUR 3 microcontroller with 10x the speed of these old things.

These days a 10c microcontroller is 20x or 50x faster than "those old things" when operating on bytes, and more for 32 bit values, and can easily emulate them at full original speed. RAM size is limited at those levels though, unless ZX81 is your thing. You have to go up to ~50c to get 64k RAM e.g. CH32V307. Hmm wait that's in qty 1000 ... seems you have to pay around $1.50 each in qty 10. Yeah, ESP32 is an option at that level too. Or RP2040/RP2350.

[Benta]

Thanks.

ChatGPT did googling for me and figures this is what I'm after:
https://www.mega-micros.co.uk/

The downside is... its "Email the guy for quote" ordering affair.

If that's how you want to go, there's a another standard way: VME 3U modular boards.
Based on 160 mm x 100 mm Eurocards with DIN 41612 connectors, the backplane basically carries the 68000 bus signals.
It's documented in IEEE-1014 and has inherent interoperability if you find some exotic interface on a flea-market :-)

But it's very much 68K-focused.
https://www.vita.com/VMEbus-FAQ

[alpher]

https://github.com/skiselev/minimax8085
I realy enjoyed building Sergey's 8085 board, cheap and easy to build, and these days you cannot go more "retro" on a cheap than intel 8085.

[paulca]

All good points/options.  I did a bit of digging and figured I have too many requirements for a single project.

I want bare metal.  To start with just the IC and build from there.  I'm talking "Blinky" and onwards.

I would say that 90% of the available kits come pretty much complete.  Sure some are self-assembly, some are a back plane, but basically you are going to spend a few evenings soldering it together and then pretty immediately it will be downloading the dev pack, test firmware/ROMs etc.

That skips a MASSIVE amount of fun.  It's like Arduino as opposed to AtMel/MChip assembler. It also dilutes the "bare metal" aspect by immediately giving me functional boot loaders, consoles, etc. etc.

I want a system that I can start with +5V and GND and watch it do nothing.  Then, put an LED on an address line and a debounced button on the clock and make it blink... or fail to.... take it up from there.

So... taking advice to NOT breadboard a 68000 (as it's a special 24 address lines and 16 wonky, intermittent breandboard, data lines kind of tedious)

I bought a genuine (I hope) second hand, tested, Zilog Z80A original.  It can be my "Blinky".  It can be my switches, buttons and LEDs project.  Then I can do the other fun part with it.  Take a modern MCU and emulate the expensive parts like RAM and ROM.

I'm not going to go looking for a circuit example, except in the datasheet.  I want to see how far I can get before I need to start googling solutions and when I google it will be "How do I solve this specific issue", not "Give me a working computer ChatGPT".

That part taken care of the 68000 can go straight to PCB.  I will need to pick and choose between the modular options.  The Mega-Micros thing is a bit jank, you have to like email him and ask and arrange PayPal payment.  No gerbers.

The style however fits.  I can take the CPU PCB board, put the 68000 in it's place and then start adding components while tagging everything else with probes or harnesses.  When I'm done torturing the CPU into life bit by bit I can move onto the other boards. 

Depending on the cost of the boards and how many there are I could get 2 or 3 of each and butcher them.

However, having the ability to carry on and add, say, a "modern interface" board with USB and maybe even networking later it would be nice to follow an "eco-system" where some of the harder work is already done... just not forced on you from the start.  Baby steps have to be available, even if the "system" takes me to the moon ultimately.

On the "Just use an MCU".  Already done that.  I've bare boned, bare metalled, Arduinos, ESPs, STMs.  Usually they don't take much more than power and peripherals.  Maybe a cap or two.  "This" project is about what happens inside the MCU.  You could say I'm just building my own macro-controller-unit.

[brucehoult]

I bought a genuine (I hope) second hand, tested, Zilog Z80A original.  It can be my "Blinky".  It can be my switches, buttons and LEDs project.  Then I can do the other fun part with it.  Take a modern MCU and emulate the expensive parts like RAM and ROM.

You can't single-step one of those like you can a 65C02. The NMOS Z80 and 6502 need to have the clock running at a certain minimum speed (10s of KHz?) all the time to not lose register contents. The 6502 has a RDY signal which can be held low to stop the 6502 fetching instructions and pulsed hi for 1 cycle to allow the CPU to execute one instruction, which does allow tracing program flow but doesn't allow monitoring every instruction and load/store byte like stopping the clock on the 65C02 does. I don't know if the Z80 has a similar signal.

[pcprogrammer]

"This" project is about what happens inside the MCU.  You could say I'm just building my own macro-controller-unit.

I would say, get yourself a FPGA board and play with that. You can even write your own CPU from scratch. A board like the Tang Primer 20K offers immense possibilities. https://wiki.sipeed.com/hardware/en/tang/tang-primer-20k/primer-20k.html

You can get it from Aliexpress: https://www.aliexpress.com/item/1005004653308809.html

It uses the same FPGA core as the Tang Nano 20K but provides a lot more IO pins to play with. The core board with the extended dock board is more expensive than the Tang Nano 20K, but I wish I had spend the extra 25 Euros.

[pcprogrammer]

I bought a genuine (I hope) second hand, tested, Zilog Z80A original.  It can be my "Blinky".  It can be my switches, buttons and LEDs project.  Then I can do the other fun part with it.  Take a modern MCU and emulate the expensive parts like RAM and ROM.

You can't single-step one of those like you can a 65C02.

You sort of can if you use the "wait" pin. https://z80project.wordpress.com/2014/02/16/single-step-instruction-circuit/

[brucehoult]

I bought a genuine (I hope) second hand, tested, Zilog Z80A original.  It can be my "Blinky".  It can be my switches, buttons and LEDs project.  Then I can do the other fun part with it.  Take a modern MCU and emulate the expensive parts like RAM and ROM.

You can't single-step one of those like you can a 65C02.

You sort of can if you use the "wait" pin. https://z80project.wordpress.com/2014/02/16/single-step-instruction-circuit/

So, similar to the 6502 RDY which I wrote about as an edit to my previous comment while you were writing yours.

Neither one will allow you to observe each instruction and data byte read/write like Ben Eater shows with 65C02, just stop before the next instruction execution.

[Doctorandus_P]

You can't single-step one of those like you can a 65C02. The NMOS Z80 and 6502 need to have the clock running at a certain minimum speed (10s of KHz?) all the time to not lose register contents. The 6502 has a RDY signal which can be held low to stop the 6502 fetching instructions and pulsed hi for 1 cycle to allow the CPU to execute one instruction, which does allow tracing program flow but doesn't allow monitoring every instruction and load/store byte like stopping the clock on the 65C02 does. I don't know if the Z80 has a similar signal.

One way of single stepping, is to not modify the clock at all, but (ab-) use an ISR. The goal is to retrigger the ISR before it exits. In that case many CPU's execute exactly one instruction before going into the ISR again, except if another ISR is pending also. Further details vary on architecture of course.

And I really don't care whether a uC costs 50ct or EUR5. Lets see:
EUR 500 for my agilent scope.
EUR 600 for my PC, Ryzen 5600G, bought during the corona crisis.
EUR 1000 for my monitor (nice big one!)
EUR 1000 or so for all the other lab equipment. (Power supply, soldering iron, function generator, etc)

And then, whatever uC I choose, it's going to take me 100 or more hours to get familiar with it. The cost of the uC is completely irrelevant to that. I do like to keep initial costs somewhere between EUR5 and EUR10. I bought over 10 Black pills (also during corona when they were more expensive. I think each was EUR 7.5, but I've got plenty of spares for when I let the smoke out of a few.

Cost optimization only becomes an issue when you're going into production, but below quanity 100 it's still negligible. I pitty all the fools struggling with not enough I/O pins on an attiny84. It wastes so many hours during development if you don't have a bunch of spare pins (and a uart / SPI, etc) for debugging, or have to multiplex your application with the programming wires. But when you're still doing old school retro computers, you're not afraid of a few extra pins anyway 

[brucehoult]

And I really don't care whether a uC costs 50ct or EUR5. Lets see:
EUR 500 for my agilent scope.
EUR 600 for my PC, Ryzen 5600G, bought during the corona crisis.
EUR 1000 for my monitor (nice big one!)
EUR 1000 or so for all the other lab equipment. (Power supply, soldering iron, function generator, etc)

Using a retro microprocessor or 10c microcontroller is not a decision made for rational economic reasons in the first place so none of that is relevant.

It's for the fun and/or challenge of getting the most out of limited resources.

Even at the $5 level now I'm using a board with a 1 GHz 64 bit CPU with length-agnostic vector processing (with 32x 128 bit registers that you can gang as 8x 1024bit registers) running full Linux in 64 MB RAM (enough for Ubuntu server), and with a 2nd 64 bit 700 MHz "microcontroller" for the real-time stuff. And an 8051 if you really want (it's there to handle the GPIOs).  Bump that to $9.90 and it's got 512MB RAM and an Arm A53 core as well.

[robert.rozee]

don't think anyone has mentioned this one yet:

https://github.com/SuperFabius/Z80-MBC2
https://hackaday.io/project/159973-z80-mbc2-4ics-homemade-z80-computer
https://j4f.info/z80-mbc2


it is called the Z80-MBC2, and is a 4-chip implementation that can run CP/M. the four chips are:
- CMOS Z80 processor
- 64k or 128k SRAM chip
- atmega32A as boot ROM emulator, I/O controller, etc
- 74HC00 as glue logic

there is some discussion here:
https://www.thebackshed.com/forum/ViewTopic.php?TID=10957
as well as numerous other places online.


cheers,
rob   :-)