Tynemouth Software Launches Minstrel Issue 3 Sinclair ZX81-Compatible Microcomputer Kit
With 32kB of built-in RAM, the board can be used standalone or as a drop-in replacement in failed Sinclair ZX81s and Timex Sinclair 1000s.
Tynemouth Software has released the third revision of its Minstrel Sinclair ZX80-compatible microcomputer kit, and it comes with one significant upgrade: It's now Sinclair ZX81/Timex Sinclair 1000 compatible, too.
"This is a ZX81-compatible Z80-based eight-bit computer kit with 32K RAM," Tynemouth Software explains of the "Minstrel Issue 3" design — the latter a considerable upgrade from an unexpanded Sinclair ZX81, which launched in the UK in 1981 with just 1kB of on-board 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.
"The Minstrel Issue 2 was a clone of the ZX80 design. As such, it was limited to either displaying a screen, or executing code," the company continues — a disadvantage of the original Sinclair ZX80 design, too. "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 Issue 3 adds the slow mode to allow ZX81 compatibility. The RAM has 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."
Other improvements include a reduction in chip count, resulting in only four additional components being required over the Minstrel Issue 2 despite the new features and the retirement of hardware-to-find parts in favour of more common components. It's even possible to use the Minstrel Issue 3 as a direct drop-in replacement for a failed Sinclair ZX81, as the PCB is compatible with the original case and can use the original membrane keyboard, a modern recreation, or a tactile switched keyboard.
More information is available on the Minstrel Issue 3 Tindie page, where prices start at $20 for the bare PCB.
