Issue 2 boards are available now, more info here.
Here is a new ZX80 clone that I have called the Minstrel. It is a fairly accurate clone electrically to the ZX80, using the same chips and the original schematic with only a few concessions to the modern world. All the parts are the same, the part numbers and pins are the same, other than the ROM and RAM, I've only added a few extra decoupling capacitors and a one resistor / one transistor composite video amplifier.
The two 2114 RAM chips have been replaced with a single 62256 chip. This is wired for 16K. 32K is possible, but would require changes to the decoding logic, 16K just needed additional address lines wiring up. The 24 pin mask ROM or 2532 EPROM used in the original has been replaced by a 28 pin ROM socket which can accept a 27C64 up to a 27C512. Upper address lines are tied high, but two 8K ROM images can be selected by a jumper, allowing original 4K ZX80 ROM or 8K ZX81 ROM to be selected.
Grant Searle's excellent site), or I had transcribed it wrongly in my PCB design (possible), or messed up the build (also possible).
Issue 2 Minstrel boards)
Paul Farrow's website, including PacMan and Space Invaders.
Minstrel Issue 2 blog post)
Thanks to Geoff Wearmouth for reminding me these are typed directly on the ZX80, as per the label on the case. I've added that list to the silk screen on the next revision of the board.
PRINT PEEK 16388+256*PEEK 16389
Yes, the top of RAM is 32768, meaning 16K is working. Not sure if these simply won't work without the ZX81 fast/slow mode NMI changes? I need to investigate further.
- ZX81 fast/slow mode NMI circuit
- Full 32K RAM (at 8K-40K for high resolution graphics mode compatibility)
- Fix composite video with back porch black level setting by changing line counting logic
- Reduce chip count and replace less common chips
- Add input amp to improve tape recorder input
- Add reset switch
- Consider edge connector, probably not.
- May look at joystick connector instead - but is there any software support?
- Surface mount at this stage, at least one more through hole revision before size reduction
- FPGA, lets stick with real chips for the moment
- Jupiter Ace / ZX Spectrum video generation - the ZX81 timings would change too much
- SD card disk drive - maybe?
- HDMI output - probably not
- AY3 sound chip - again, is there any software that would use it?
- 3D monster maze in ROM - hmm, possibly.
The issue 1 boards are now sold out. Issue 2 is available now. More issue on the issue 2 board.
If you want to support this blog, you can donate via Patreon or Paypal, or buy something from my store.