flowchart TB
  KB["Keyboard
ROM 028E"] --> PL
  PL["Player engine
80D3 / 8D9A"]
  AN["Ant engine
8BD1"]
  GR["Grenade
entity 7"]

  PL <--> CITY
  AN <--> CITY
  GR <--> CITY
  PL -.->|"position"| AN
  PL -->|"throw"| GR
  GR -->|"sleep = 255"| AN
  AN -->|"bite"| MSG

  CITY[("City map
C000 · 16 KB")]
  CITY --> CULL["Cull → window
B180 · 672 B"]
  CULL --> BLK["Stamp blocks"]
  ENT[("Entities
B480 · 8 × 16 B")] --> SPR["Blit sprites"]
  PL --> ENT
  AN --> ENT
  BLK --> BUF
  SPR --> BUF
  BUF[("Buffer
A000 · 4 KB")] -->|"LDIR"| SCR["Screen
4000"]
  MSG["Message printer
8E02"] --> SCR
  VAR[("Score & ammo
B420")] -->|"code 7E"| MSG
  GR --> VAR