plasticbugs.bbcmicro - 0.3.0

plasticbugs Sep 22, 2026

BBC Micro Acorn, 1980

The BBC Micro Model B: a 6502 at 2MHz, 32K, MODE 0 to 7, four-channel sound, and an 8271 disc controller reading .ssd and .dsd images.

ROMs are not included: build one from your own MAME bbcb romset with mra_build.py and bbcmicro.mra.

LOADING A DISC

• Core Settings, Load Drive 0
• Auto-boot disc: BREAK boots it, as SHIFT+BREAK does on a real machine
• No !BOOT gives File not found: type *CAT to list it, then *RUN name or CHAIN “name” for a BASIC loader

CONTROLS

• L+R+Select on-screen keyboard
• L+R+Start BREAK
• D-pad and A B X Y press keys; pick which in Core Settings. Eight d-pad sets, including CAPS and CTRL
• Joystick: the pad drives the analogue port, A and B fire
• On the keyboard the d-pad moves a whole key, A or B presses, and the modifiers latch. SHIFT swaps the legends to the punctuation it types

SIDEWAYS RAM

• Fits a 64K board: banks 4 to 7, kept across BREAK
• Banks 4-7 are where software of the period looks. A bare Model B cannot reach them at all
• Switch with STA &FE30 from a routine in main RAM, with SEI; BASIC cannot, it is in bank 3
• No *SRLOAD: that is a Master command, this is a Model B