Lestnica (Лестница) — Annotated Disassembly

An educational, byte-exact annotated disassembly of Лестница ("Ladder") — an Intel 8080 game written in 1987 for the Radio-86RK (Радио-86РК) home computer. The original game is credited on the title screen to Симонов Ю.Б. (Simonov Yu.B.).

Title / menu screen	In-game

▶ Play it online in an RK86 emulator: rk86.ru/beta/?file=LESTNICA.GAM

Purpose

This project exists purely for historical preservation, study, and education — to understand how 8080 games of that era were structured, how compilers of the time generated code, how RLE-compressed screen data was laid out, how self-modifying code was used for difficulty settings, and how the RK86 KOI-7 character set encoded both Russian text and block-drawing graphics.

The annotations, scripts, and documentation added here are the work of contributors to this repository and are released under the MIT License (see LICENSE). The annotation layer is a derivative work of analysis; it contains no new original game content.

The underlying game binary LESTNICA.GAM (and its tape-format counterpart LESTNICA-TAPE.GAM) is the original 1987 work of Симонов Ю.Б. and remains the property of its original author(s). This repository does not claim any rights to the original binary. If you are the original author or rights holder and wish to have the binary removed, please open an issue.

Build & verify

The assembled output must match LESTNICA.GAM byte-for-byte.

just ci        # build + test (byte-identical round-trip)
just build     # assemble only
just test      # diff assembled binary against LESTNICA.GAM
just disasm    # regenerate lestnica.asm from LESTNICA.GAM (overwrites!)

Requirements: bun (for bunx asm8080), just, python3.

Main artifacts

file / dir	description
LESTNICA.GAM	original game binary (7712 bytes, org 0100h) — unmodified original work
LESTNICA-TAPE.GAM	tape-format copy (5-byte header + 3-byte trailer) — unmodified original work
lestnica.asm	annotated source (assembles byte-identical to LESTNICA.GAM)
lestnica.lst	assembler listing with addresses and symbol table
lestnica.bin	assembled output (generated; gitignored)
disasm.py	single-file Python Intel 8080 linear disassembler (used to seed lestnica.asm)
render_screen.py	level / title-screen extractor — decodes RLE screen data into 78×30 ASCII-art text files
levels/title.txt	rendered title/menu screen
levels/level_A.txt, B, C, D, E, F, G	rendered playfields for the 7 unique levels
info/rk86-charmap.md	RK86 character-set reference (ASCII + Cyrillic + block glyphs)
CLAUDE.md	conventions, known game mechanics, and findings accumulated during analysis
Justfile	build recipes

Highlights of what's been decoded

• Full code structure: menu handler, new_life state reset, main tick loop, movement handlers, BCD score arithmetic, collision checks against known tile glyphs
• 32-bit LFSR PRNG at prng_next (seeded 5A 34 17 71)
• RLE screen-data compression scheme and paint_screen decoder
• Level-pointer table structure (7 unique levels, 27 entries across 7 "rounds")
• Self-modifying code sites for difficulty and speed settings
• Complete tile glyph semantics from the in-game legend

See CLAUDE.md for the full catalog of findings.

License

• Annotations, scripts, and documentation in this repository: MIT License (see LICENSE).
• LESTNICA.GAM and LESTNICA-TAPE.GAM: © 1987 Симонов Ю.Б. (Simonov Yu.B.) — all rights reserved by the original author. Included here solely for educational and preservation purposes.