A ZX81 compatible Z80 based 8 bit computer kit with 32K RAMDesigned by Tynemouth Software in United Kingdom
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What is it? This is a ZX81 compatible Z80 based 8 bit computer kit with 32K RAM. It evolved from the Minstrel Issue 2 ZX80 clone. Adding NMI Fast/Slow mode makes it ZX81 compatible, so it can run m...Read More…
This is a ZX81 compatible Z80 based 8 bit computer kit with 32K RAM. It evolved from the Minstrel Issue 2 ZX80 clone. Adding NMI Fast/Slow mode makes it ZX81 compatible, so it can run most ZX81 / TS1000 or ZX80 software. The RAM has been upgraded to 32K and supports most high resolution graphics mechanisms used on the ZX81. The design has been refined to reduce the chip count, and it is now using 74HC series logic chips.
This is an 8bit Z80 based computer, with 8K of ROM, 32K of RAM and a 3.25MHz Z80 Processor. Input is via an 8x5 matrix keyboard (see below for options), output via composite video. It is programmed in a simple version of BASIC. 10 PRINT "HELLO WORLD", 20 GOTO 10, RUN.
The Minstrel 2 was a clone of the ZX80 design. As such, it was limited to either displaying a screen, or executing code. This lead to the screen flickering when ever a key was pressed, or going blank when code was running before displaying the results. The later ZX81 added a 'slow' mode which allowed code to run in between drawing parts of the screen, which allowed the display to remain on unless the code specifically switched into 'fast' mode where it acted like the ZX80 and turned the screen off to allow code to run much faster.
The Minstrel 3 adds the slow mode to allow ZX81 compatibility. The RAM bas been expanded to 32K (positioned from 8K-40K in the memory map, mirrored in the top 16K for the display file) with support for various high resolution graphics modes. The design is based on the original ZX80 with Grant Searle's NMI slow mode modification, but has evolved quite a bit since then and is now a design of it's own.
Much has been done to optimise the design and reduce the chip count. The extra features have only added four chips over the Minstrel 2. Reliance on some less common parts (such as the 74LS05, 74LS93 and 74LS365 etc.) has been removed with those replaced by more common parts. The design will now run with 74HC series logic, so as an all CMOS design, with nice clean logic signals and reduced power consumption. The board runs at around 60mA, so it can be powered by a 7805 regulator without need for a heatsink. You can fit one if you need to use more power via the expansion port, or fit a 7805 switch mode replacement.
The composite video buffer has been improved, so this should be able to be connected to any TV with a SCART connector or composite video input. 50/60Hz frame rate is available via a PAL/NTSC jumper. Clock synchronisation of the output pixels to ensure consistent pixel width (which was not the case with the ZX80), and a digitally timed backporch signal added (which was missing in ZX80s and early ZX81s). There is an option to add a greyscale crosshatch border around the edges of the screen, something the ZX81 never had.
The board is the same form factor as a ZX81 board, so can be used as a direct replacement for a faulty ZX81. A superior replacement in many ways in that it is less fragile than the ULA based original, and also adds the extra RAM and composite video output.
What options are available? This kit is available in several versions
For ZX81 Case This version of the kit includes all the parts necessary to produce a board which will fit inside a ZX81 case (not supplied). Optionally a replacement ZX81 membrane can be included if the existing one is damaged (it is a common fault, look for short, brittle or cracked membrane tails).
Open board with Tact Switch Keyboard This version has the board out in the open with the Minstrel tact switch keyboard with 8K BASIC keyboard overlay, and optionally a Minstrel ZXpand.
Add a Minstrel ZXpand kit to go with the Minstrel 3. This is an SD card reader and joystick interface. The version here is the one with the pin header which is soldered directly to the Minstrel 3 expansion connector. See the separate Minstrel ZXpand listing for full details or if you want the further options.
As above, but with an SD card preloaded with some sample software to try for you to try.
All the parts required to build this are still in production and available new from many suppliers. No 'new old stock' parts are required. The kits are supplied with all new Texas Instruments 74HC series chips, Zilog Z80 CPU, Alliance RAM and an Atmel OTP EPROM. The resistors supplied with the kits are 5% 1/4W resistors with 4 band markings, these are more in keeping with the 8-bit computer theme than the more modern 1% 5 band blue resistors, although these can of course be used if you prefer.
The kit requires assembly. All parts are 0.1" pitch through hole parts, basic soldering skills are required, although this is not suitable for an absolute beginner.
Finally, if you are reading this on ebay, then someone has copied the board and is selling unauthorised clones and has just cut and pasted this text as they did with the Minstrel 2. Please support the work that goes into developing this range of products and don't buy the knock offs.
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International shipping via DHL or Parcelforce. Limited service is available from both services currently, so the best option will be selected.
David | May 21, 2020
Randall | Feb. 15, 2020
James | Jan. 18, 2020
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