It was the early 1990s and many computer magazines advertised the Gerton Lunter's Z80 emulator. A full shareware emulator of the ZX Spectrum microcomputer that ran smoothly on those powerful 286 to 20 Mhz of the time. For me, who until then had only programmed in high level languages, "putting" a computer into another one seemed complicated.
I have continued to be interested in emulators and their development since then, and even started to emulate different devices, mainly in C and C++. So the slow but logical evolution was to write one of my own and, because of my growing interest in Node, to do it in JavaScript. A language interpreted and in theory inappropriate for the task. The challenge was also to write everything from scratch, without consulting the code of the emulators already existing in this language, or using already available Z80 processor engines. Start emulating all the instructions and add the rest of the components later: a small ULA, keyboard, sound, the ability to load files, etc.
In this project I have been accompanied by two books: Código máquina del ZX Spectrum and The Undocumented Z80 Documented, and a great amount of code released from"veteran" emulators that I have used to solve many issues. As a result, the process has been less frustrating than I first thought and the result is a simple emulator still full of bugs for the ZX Spectrum 48K. Functional but far from finished.
About the ROM: Amstrad have kindly given their permission for the redistribution of this copyrighted material but retain that copyright.