flowchart TD
  A["message(n)"] --> B["HL = 9000
scan for FF, n times"]
  B --> C["IY = 5C3A
restore ROM system variables"]
  C --> D{"next byte"}
  D -->|"FF"| E["done"]
  D -->|"≥ 80"| F["play sound
id = b & 0F, repeat = b >> 4"]
  D -->|"7D"| G["recolour the viewport"]
  D -->|"7E"| H["print memory location
as decimal"]
  D -->|"else"| I["RST 10h
ROM character output"]
  F --> D
  G --> D
  H --> D
  I --> D