jsbeeb - Javascript BBC Micro emulator

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By Matt Godbolt, based on Sarah Walker's b-em: huge thanks to her for open sourcing it, and to Richard Talbot-Watkins for his help and support. The Acorn Atom emulation is Andrew Hague's. The cycle-accurate emulation owes a great deal to the fantastic Visual 6502 project, who are well worth a donation. The disc loaded by default is the amazing Elite, made available by Ian Bell.

Source on GitHub. For more on the BBC, and people to talk to about it, try the StarDot forums. Works best in Chrome or Firefox. Icons are from Bootstrap Icons (MIT).

An emulator for the BBC Micro, a popular home computer in 1980s Britain. It emulates the BBC B and the Master, and also the Acorn Atom that came before them. Choose which by clicking the model name at the top left.

The default disc is Elite, a pioneering 3D space trading game. Discs are booted by pressing SHIFT and BREAK. The BBC's keyboard differs from a modern one, mostly in where the symbols are; the layout here currently assumes a US keyboard.

Handy key mappings

BBC	PC	macOS
F0	F10	F10
BREAK	F12	Right ⌘ + F12
COPY	End	Right ⌘ + F11
* :	" '	" '
CAPS LOCK	CAPSLOCK	See notes
Debug	Ctrl-Home	Ctrl-Home
Pause	Ctrl-End	Ctrl-End
Full speed	Ctrl-Insert	Ctrl-Insert
Rewind	Alt-PageDown	Alt-PageDown

While paused, g resumes and n runs one frame. In the debugger, g resumes, n steps one instruction, m steps over a call, o steps out of one, t toggles a breakpoint on the highlighted instruction, j and k move the disassembly, b goes back to where it was, and u and i move the memory view by 8 bytes (U and I by 64).

Caps lock is unreliable on macOS: browsers never report it being released, so games that use it to move or fire don't work. Any key can be remapped from the URL.

6845 state

6845 regs

System VIA

User VIA