I would like to announce that the Minstrel Issue 3 is finally complete and available to order now.
- To be able to run 3D Monster Maze
- Add NMI based Slow mode
- Expand to 32K RAM
- Support Hi Resolution graphics
- Improve the composite video output
- Reduce chip count
- Remove dependence on analogue elements
- Replace some of the more esoteric logic chips with more common ones
- Switch to 74HC series chip
- Keep the ZX81 form factor
- Keep using only modern still in production through hole parts
- Expand the userguide to include full schematics and descriptions of functionality
This took quite a bit of work, but all things have been achieved with the Version 3.5 board. Slow mode has been added, along with a jumper to disable it if you want to run as a ZX80. The RAM has been expanded to 32K, which sits from 8K-40K, mirrored in the top 16K for display file use. The video has been improved with a digitally timed backporch and uniformly sized pixels. I managed to get rid of chips like the 74LS05, 74LS93 and 74LS365, replacing those with more common parts. With all the new functionality, the chip count is now 25 chips, only four more than the Minstrel issue Two. (the original Minstrel Issue 2 will still continue to be available for those who want a pure ZX80 design).
*At least it runs all the ZX81 software I have tried. It doesn't support things like chroma or UDGs that required additional plug in boards, but does support WRX and psuedo high res that will run on a ZX81 with the correct RAM configurations and /WR pulled high. If you have anything you would like me to test, let me know.
2023 Update: Minstrel 2, 3 and 4th PCBs, kits and built and tested boards are available via my SellMyRetro store - https://www.sellmyretro.com/store/tynemouth-software
See this post for more information - http://blog.tynemouthsoftware.co.uk/2023/08/minstrel-3-pcbs-kits-and-built-boards.html