The VC-3 is a system, running on the SD-8516.

I guess this interrupt system is part of the KERNAL, so should be more “VC-3” as it is system software. What follows is a simple list of the interrupt, what it does, it's calling parameters and it's return codes. I guess this should be called “Stellar BIOS V1”.

Each INT subsystem has it's own convention. However, the INT 05h system was done first so it represents a general convention you can expect going forward.

Parameters: - Function number: `AH` - Small values: `AL`, `B`, `C` - Pointers: `ELM`, `ELD`, `ELX` (EL-group)

Returns: - Values: `B` (or `A` if needed) - Status: Carry flag - Updated pointers: Same register (ELM/ELD)

Example Code:

LDAL #'A'
LDB #1234
LDAH $11        ; VAR_SET
INT $05

LDELD @string
LDAH $62        ; IO_GETNUM  
INT $05
; B has parsed number

  ; ============================================================================
  ; INT 10h - VIDEO SERVICES
  ; Stellar BIOS Video interrupt handler
  ; ============================================================================
  ; Function dispatch via AH register:
  ;   AH=00h: Set video mode
  ;   AH=01h: Set cursor shape (reserved)
  ;   AH=02h: Set cursor position
  ;   AH=03h: Get cursor position
  ;   AH=0Eh: Write character at cursor (teletype)
  ;   AH=0Fh: Get current video mode
  ;   AH=13h: Write string at cursor
  ;   AH=14h: Scroll screen up
  ;   AH=15h: Clear screen
  ;   AH=16h: Get video parameters (rows, cols)
  ; ============================================================================

• Returns: AL is 00 on success, 01 if the mode failed to init.

Available modes:

• Mode 0: 22×23 console
• Mode 1: 40×25 console
• Mode 2: 80×25 console
• Mode 3: still thinking, graphics, or superterminal? 1280×800 “128×40“font via 10×20 charset??

• returns character code in AL and keyboard flags in BL.

• returns character code in AL, keyboard flags in BL, and time spent waiting in ms in C

• returns keyboard flags in AL.

• returns the number of keys waiting in AL. I.E. 0=no keys available, 1+= has keys waiting.