Commodore 64 · 1984 · Novagen Software

About this page

Footprint

Every byte of the C64's 64 KB, one pixel each, 512 to a row. Lit pixels are what this game is: its code, graphics, level data, sound, text, tables and variables, exactly where they sit in memory. Dim areas are screen and working memory; dark is unused.

Status

Contributors

• air (9 commits)
• Paul Woakes — programmer

Other places to love this game

• wiki
• manual

What the game does, and where we found it

Read this before annotating code. What the game is documented to do, with verification status against the binary. Statuses: open (documented, not found yet), traced (in the code, could not be exercised; say what was tried), confirmed (in the code, consistent with the emulator), live (observed directly), differs (the code does something else). "Absent" is not a status.

Sources:

• C64-Wiki, https://www.c64-wiki.com/wiki/Encounter, read 2026-09-20
• Wikipedia, https://en.wikipedia.org/wiki/Encounter!_(video_game), read 2026-09-20
• The Novagen manual as transcribed at http://c64-games.blogspot.com/2009/11/encounter-manual.html, read 2026-09-20
• Finnish Retro Game Comparison Blog (C64 vs Atari 8-bit), http://frgcb.blogspot.com/2015/09/encounter-synapse-software-1983.html, read 2026-09-20
• The contributor's transcription of the original C64 manual, https://github.com/air/encounter#original-c64-manual, read 2026-09-20
• The game itself in the emulator, 2026-09-20 (title screen text, first minute of level 1)

The sources disagree in places: the wiki says "seventeen UFO types" and "10–19 enemies per level"; the comparison blog says two adversary types (saucers and homing drones) with two new saucer attack strategies per level; the manual says eight levels. Each is a claim to check, not a fact.

Features

Title screen and setup

Play

Between levels

Cheats reported

Beyond the documentation

Found in the code, not in the manual.

• The picture is a text screen. The raster chain repaints the background colour per band (sky, three horizon lines, ground) and every object is composited into dynamically allocated characters from 32 pre-scaled scripts per family ($9600/$9700, renderer $AD76); the ground half of the view is the sky half reflected by copying the screen rows with the codes inverted and byte-reversing the charset ($B1EC). The view is double-buffered ($6000/$4000 and $6400/$5000).
• Joystick fire starts a game from the title screen ($9D13).
• The enemy count, level, score and shields on the status row are the game's own copies: the shield count exists only as the screen digit at $6026.
• An idle timer $58 (256-frame units) makes a homing missile come after 24 periods without a kill or shot, and makes a saucer leave after the same time.
• The game checks for PAL at $9DEC; on an NTSC machine it draws the title screen and hangs at $DBE8 (tested live; see facts.md, Oddities).

Open questions

• Whether this copy is the original Novagen release or a crack: the cruncher is scene-style but no cracktro or trainer appears.

How the analysed state was reached

How to get from the contributor's own copy to the analysed state. Someone else must be able to follow this exactly.

The image

ENCOUNTR.P00, a PC64-format program file (26-byte C64File header, filename ENCOUNTR, then a PRG). Stripping the header gives a 20,263-byte PRG loading at $0801 ending at $5726. The BASIC stub is one line, 1001 SYS 2066, so the machine-code entry is $0812. The program is crunched: the loader at $0812 installs a decruncher in the stack page ($00FA–$01A0) and the tape buffer ($0333–$03D9) and jumps to $0100. No trainer, cracktro or menu appears; the title screen credits "Paul Woakes", "© 1984 Novagen Software". Whether this is the original release or a cracked copy is unknown: the cruncher is scene-style (self-modifying page copy, $01 = $30 all-RAM during depack) and the title screen shows nothing beyond the publisher's own credits.

The kit works from work/encounter.prg (the PRG with the P00 header removed: tail -c +27 encounter_0_original.p00 > encounter.prg).

From power-on to play

1. Autostart work/encounter.prg (vice_autostart with the path). The loader depacks in under a second; the title screen appears with SCORE / LAST SCORE / HIGH SCORE and F5 NOVICE, F7 BEGIN GAME. Turn warp mode off (autostart leaves it on).
2. No loader menu. Snapshot: work/title.vsf at the title screen.
3. Press F7 through the keyboard matrix, held about 2.5 s (the game scans the keyboard itself via the KERNAL SCNKEY and reads $C5; a short tap can be missed). Play begins immediately: a first-person cockpit over a green plain with a blue sky, status row 0000000 L1 E11 54 (score, level 1, enemies remaining, a countdown), crosshair in the centre, black pillars on the horizon.
4. Snapshot: work/play-level1.vsf, taken a few seconds into level 1 with no joystick input given yet. This is the image the disassembler is loaded on.

F5 selects NOVICE before F7; the snapshot was taken at the default (not novice) setting. Not yet explored.

Steady state

Observed in play-level1.vsf:

The IRQ handler at $B34E is a chain of short stages: each stores a colour into $D021, rewrites $0314 to the next stage and $D012 to the next raster line, acknowledges, and returns. That is how the sky, horizon and ground bands are drawn on a plain text screen.

Program counter samples during play scatter over $ADxx–$B8xx, so the main loop lives in the block under the banked-out BASIC ROM. The init code is at $9C00. Nothing is reloaded from disk: the whole game is resident after the single depack, and the title screen returns without a reload.

The loader, in a paragraph

SYS 2066 runs $0812: SEI, $01 = $30 (all RAM), copy 166 bytes from $082A to $00FA and from $08D0 to $0333, then JMP $0100. The decruncher in the stack page and tape buffer expands the packed data downwards from $55E5 over $0801 onwards, and finishes at $0960. That routine is a self-modifying page copy that moves the whole depacked image up by $3000 (every page $0D→$3D, $0C→$3C ... wrapping) and jumps to $9C00. The init at $9C00 copies 34 pages from $3E00 down to $1E00, writes the vector pair $9C3E into $8000–$8003, calls the KERNAL IOINIT, copies 160 bytes of initial variables from $8B00 into zero page $02–$A1, sets $01 = $36, selects VIC bank 1, and enters the title screen. Two checkpoints (at $0960 and $9C00) each hit exactly once on a fresh run, which is how the chain was confirmed. Not annotated further, by policy.

Emulator notes from this run

Loading play-level1.vsf back with vice_snapshot_load after a hard reset and a second autostart came back with $01 = $37, the CPU in the KERNAL screen-scroll routine and a garbage screen. Autostarting the PRG again and pressing F7 is faster and reliable; the snapshot file itself is fine for the disassembler and for offline sweeps.

The symbol map for this game is symbols.json; the listing behind the Source tab is listing.json. Write-ups, facts and symbol maps are CC BY-SA 4.0. The game itself is not hosted here.