May the 4th be with you.
Five years ago today, the Minstrel 4th was launched with that bad pun.
And now it's back, with the same bad pun.
Yes, the Minstrel 4th is back, and available now from my Tindie store.
What is it?
It is a Z80 based single board computer with 49K of RAM, 2K of video RAM and 4 banks of 13K of ROM, running at 3.25MHz or 6.5MHz (or an external clock up to 8MHz)
It is compatible with the Jupiter Ace.
What is that?
The Jupiter Ace was a Z80 based single board computer with 1K of RAM, 2K of video RAM and 8K of ROM, running at 3.25MHz.
Unlike it's contemporaries like the ZX81 and the ZX Spectrum which ran BASIC, this runs Forth. (hence Minstrel 4th, do you see what I did there?)
Forth is a very fast and powerful language, although not as easy to pick up as BASIC, it is well worth investigating.
More info on Forth can be found here:
- http://blog.tynemouthsoftware.co.uk/2020/06/minstrel-4th-quick-start-guide.html
- http://blog.tynemouthsoftware.co.uk/2023/01/some-simple-forth-programs-for-minstrel-4D.html
- https://github.com/markgbeckett/jupiter_ace
No post on Forth would be complete if it didn't show the result of the vlist command.
This shows the current vocabulary list, all the build in functions.
The default for the Minstrel 4th is black text on a white background, as it was for the ZX80 and ZX81 etc. I prefer this (it is also easier to take pictures of).
The Jupiter Ace used white text on a black background, so the inverse options is available if you wish.
The video on the Jupiter Ace was generated by a lot of logic chips forming counters and decoding logic. To simplify things, the Minstrel 4th uses a microcontroller to do the counting. The produces a more correct composite video signal with a backporch that was originally missing, and PAL or NTSC support via a jumper.
There is a 2K dual port video RAM chip to avoid multiplexing circuitry (the Ace had contended and un-contended memory access via two different address ranges, both are un-contended on the Minstrel 4th)
There is a lot of software available for the Jupiter Ace which will all run on the Minstrel 4th.
As well as some modern titles.
You can load using a standard cassette recorder, such as my favourite Sony TCM-818.
Or you can play the audio files into the ear port.
Not all PC sounds cards can cut it (low output level and fancy audio processing), but these cheap USB dongles usually work fine.
This is a great port of David Stephenson's Tut-Tut by George Beckett.
RC2014
One of the best features of the Minstrel 4th is it has an RC2014 expansion slot. This means it can use RC2014 modules to add whatever new functionality you want.
Most modules should work, apart from any that contain ROM, RAM or CPUs. The only IO port used on the Minstrel 4th is $FE. All others are available. Interrupts are used, generated by the video circuitry and used for timing, display update and keyboard scanning etc.
Minstrel 4th is designed for RC2014.
But don't just stop at one module, add a backplane and you can have loads.
The backplane 5 is a good starting point.
A lot of standard modules and backplanes can be used, some of the ones shown in the photos are:
- https://www.tindie.com/products/shieladixon/usb-keyboard-interface-for-minstrel-4th-4d/
- https://www.tindie.com/products/dr_ian_johnson/jester-ace/
- https://www.tindie.com/products/semachthemonkey/ym2149-sound-card-for-rc2014-retro-computer/
- https://www.tindie.com/products/semachthemonkey/backplane-5-for-rc2014-z80-homebrew-computer/
- https://www.tindie.com/products/semachthemonkey/digital-io-module-for-rc2014-z80-homebrew-computer/
- https://z80kits.com/shop/tynemouth-68b50-clocked-serial-port/
Many more are available, see also:
This is my current fully loaded setup.
Made up of the following parts.
ROM options
There are four ROM options available with the Minstrel 4th
1 - The standard Forth ROM
This is the standard Forth ROM, to be most compatible with the Jupiter Ace.
2 - Enhanced Forth ROM
This is a patched version of the Forth ROM by Aleksandr Sharikhin (with some extra code from George Beckett).
This adds various features, see the github for details.
This works well with a 68B50 serial card, I have designed one with a separate clock, so it can run at 7.37MHz to divide down to standard RS232 baud rates, and the Minstrel 4th can run at a different speed.
With such a card installed, you can use some of the extra words it added to access the serial port.
If you use a standard FTDI serial cable to connect this up to a PC, you can run a file server from a Python script.
On the Minstrel 4th end, you can use commands like ls to show a directory listing or tapin to open a tape file and then use the modified load command to load over serial in a matter of seconds.
There I was loading 4D Monster Maze, a modified version of George Beckett's Ace version of 3D Monster Maze with some extra features.
If you press R when the first screen appears, you will be invited to select a DIO port. I like a bit of Ronnie James Dio. Oh wait, no.
If you have one of the RC2014 Digital IO modules, then it will function as a "Rex detector" and show you how close Rex is getting.
It also support my RC2014 Joystick module so you can use a standard 9 way D joystick in various games.
Another module you might want to pick up is Ed Brindley's YM2149 sound card.
This is supported by several games, including George Beckett's updated version of Centipede.
It works with the built in speaker, but sounds great with the extra AY-3 sounds.
There is a lot of software out there, including many new games:
- https://github.com/markgbeckett/jupiter_ace
- https://www.jupiter-ace.co.uk/
- https://gldm.itch.io/
- https://petrih.itch.io/
- https://nihirash.itch.io
3 - MPF-1
The Micro-Professor MPF-1 was a single-board computer, made by Multitech in the early 1980s. It was intended as a teaching aid for learning to program the Z80.
This used a 36 key keypad and 6 digit LED display and a simple monitor program, which allowed a user to enter small machine-code programs as hexadecimal object code, and then debug and run those programs.
George Beckett has ported the MPF-1's monitor to run on the Minstrel 4th so you can try out Z80 coding with the built in assembler and disassembler to help you debug your code.
Full details can be found here:
4 - ZX80 BASIC
What?
Yes
This is a port of the 4K ZX80 Integer BASIC that runs on the Minstrel 4th.
It is compatible with most BASIC programs, but is not fully hardware compatible for obvious reasons.
I have replaced the standard ZX80 screen draw routines with a routine to copy the ZX80 display file into the Minstrel 4th video RAM. It does that every frame so this display works pretty much as it did, although there is no flicker as the display continues to be drawn by the microcontroller even when the Z80 is busy.
I have written new LOAD and SAVE routines, which show a countdown rather than wavy lines.
They keyboard matrix is slightly different, as is the load hardware, so any games that use fancy display techniques, or their own keyboard scanners or load routines will not work.
But it works well enough for Paul Farrow's ZX80 versions of Kong and PacMan for example.
- http://www.fruitcake.plus.com/Sinclair/ZX80/FlickerFree/ZX80_Kong.htm
- http://www.fruitcake.plus.com/Sinclair/ZX80/FlickerFree/ZX80_Pacman.htm
(but sadly not the recent port of Rock Crush or Rocket Man - for those you need the full ZX80 compatibility of a Minstrel 2)
- https://www.tindie.com/products/tynemouth/minstrel-2-with-keyboard-z80-based-zx80-kit/
- http://www.fruitcake.plus.com/Sinclair/ZX80/FlickerFree/ZX80_RockCrush80.htm
- http://www.fruitcake.plus.com/Sinclair/ZX80/FlickerFree/ZX80_RocketMan.htm
Options
The Minstrel 4th is available as a kit or assembled. With sockets for the main chips, but optionally for the logic chips as well.
The standard version comes with a built in keyboard, but it is also available without a keyboard, should you want to use your own, or do something else.
I did create a sticker to fit over a ZX81 membrane, if you want to do something like that.
And the board is ZX81 size, so.....
But you won't be able to use an RC2014 modules, unless you are very creative with a Dremel....
Or there is a USB keyboard interface from Shiela Dixon:
So you can use a standard USB keyboard (doesn't it look small in comparison?)
Or even a non-standard USB keyboard (yes, they are back as well)
But most people will want the standard version with keyboard.
Whenever I pack a new kit, I like to build one to test.
As always, they work first time.
Oh wait,
That's not right.
Hmmm.
About 95% of the issues come down to things like incorrect jumper settings, shorts, dry joints, missed pins, etc.
Ah, there it is.
Sorted.
I think that's enough for now. I don't think I have included as many links in a blog post ever, and I think I must be pushing the number of images as well.
The only link you really need is this one:
Patreon
You can support me via Patreon, and get access to advance previews of development logs on new projects and behind the scenes updates. New releases like this will be notified to Patreon first, if you want to be sure to get the latest things. This also includes access to my Patreon only Discord server for even more regular updates.
