The Minstrel 4th – a new Z80 board running Forth @tynemouthsw
The Minstrel 4th is a Z80 based single board computer on a ZX81 shaped board, but this one is not compatible with the ZX80 or ZX81. This one runs Forth, and is compatible with the Jupiter Ace.
I redesigned the video circuitry in a much simpler way, without any 1K resistors. One concession though is the introduction of a microcontroller to do the counting. It’s is just running a state machine counting through the cycles and generating the video sync and timing. Doing pretty much what a 6845 does in a PET.
With that the picture is considerably improved and there is no display corruption. With the extra control of the timing, I was able to add a back porch signal. This was originally missing on the Ace, but was much less of an issues with it’s black text on a white background. I added a jumper so you can select black text on a white background instead. There is also a PAL/NTSC 50/60Hz jumper rather than having to have separate boards like the Ace did.
The Minstrel 4th is able to run Forth and Jupiter Ace programs just like a real Ace would. And the video output looks great.
… the Z80 is free to run user code all the time, and can use any add ons that a Z80 can, so I thought why not give this an RC2014 bus connector, then it can use all the RC2014 expansion modules.
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