An explorer crosses the jungle picking up treasures, against a clock that runs out. Everything on this page comes from reading the code that does it.
The scene you are in is the content of one byte of RAM, 0xE222. When the player's X reaches the right edge —0xE7— it is put at 0x19, the other side, and that byte is stepped once (0x9CBE). On the left, at 0x16, the same happens in reverse with the inverse function (0x9CF9).
The step runs through 255 values before repeating, so the world is a ring of 255 screens in a fixed order: the game always starts on the same scene and the next one is always the same. Nothing is random, and there is no list of screens in the cartridge.
When a scene is built (0x9EE6), three things are read from the byte:
| bits | what they choose |
|---|---|
| 6-7 | the scenery: which of the four landscapes is drawn (0x9F91) |
| 3-5 | the kind of scene, 0 to 7 (0x9EFB) |
| 0-2 | the variant within that kind (0x9EEF) |
Bits 3-5 pick one of eight routines through the table at 0xAEB4:
| Kind | Routine | What it is | How many |
|---|---|---|---|
| 0 | 0xA9AA | pits in the ground, with a ladder to the underground | 31 |
| 1 | 0xA9AA | the same: both entries point to the same place | 32 |
| 2 | 0xAC7C | a tar pit, with a vine | 32 |
| 3 | 0xAC6B | a water pool, with a vine | 32 |
| 4 | 0xAD75 | a lagoon with three crocodiles, with a vine in 16 of them | 32 |
| 5 | 0xADF6 | the treasure scene, the only one that scores | 32 |
| 6 | 0xAE04 | tar with a vine | 32 |
| 7 | 0xADE8 | water, no vine | 32 |
The share-out is almost uniform because the ring visits the 255 non-zero values: only kind 0 gets one scene fewer.
Kinds 0 and 1 share their routine; what splits those 63 scenes in two is bit 7 of the register, which 0xA9AA reads on its own to decide where the bounce box goes —class 10, centred at 0xD8 with the bit set and at 0x31 with it clear— and whether one pit or three are drawn. The ladder does not move: both branches draw the same cell script, 0x8F06 (0x8D4A and 0x8D5D).
Kinds 2 and 3 are the same drawing in a different colour: 0xAC7C writes 1B 1B 1B into the colour table —a black pool, tar— and 0xAC6B writes 7B 7B 7B —cyan, water—.
The three crocodiles sit at X 0x50, 0x6F and 0x88 (0xA828) and open their mouths every frame (script at 0xAFD8); with the mouth open their collision box grows (0xA812).
The vine is set up by monta_la_liana (0xAE38), and four places call it. Three are the plain calls in kinds 2 (0xAC88), 3 (0xAC77) and 6 (0xAE04). The fourth one works differently: the tail of the lagoon, 0xADDE, dispatches through the table at 0xAE94 keyed by the variant instead of the kind, and that table holds monta_la_liana at its entries 2, 3, 6 and 7 —the other four are a bare ret—. ld hl,0AE94h appears exactly once in the whole cartridge and the kind 4 routine has no other entry point, so that is the only way in.
Since the ring visits the 255 non-zero values, 16 of the 32 lagoons have a vine and 16 do not, and the scenes with a vine are 112 of the 255, not 96. Of the pool family, the one left without any is kind 7.
You can check it without playing and without reading more code, because they are the same scene with the variant changed: with 0xE222 = 0x26 the rope hangs from the tree, and with 0xE222 = 0x24 it is not there. make capturas takes both screenshots.
The treasures are exactly the 32 scenes of kind 5: kind 5 is the only one dispatched through the table at 0xAEA4, which holds four routines repeated two by two, and the eight variants share out four scenes each. One treasure of each class eight times:
| Routine | Worth | How many |
|---|---|---|
| 0xAC11 | 2000 | 8 |
| 0xAB51 | 3000 | 8 |
| 0xAB1B | 4000 | 8 |
| 0xABB7 | 5000 | 8 |
Four drawings: the money bag, two bars and the ring. The two bars share their colour (0x4B at 0xAE90 and 0xAE92): the pattern tells them apart.
8 × (2000+3000+4000+5000) = 112000 points spread over the world. The score starts at 2000 (0x8A28), so the ceiling of the game is 114000.
What you have taken is remembered in 32 bits: 0xE21D-0xE220, one byte per class and one bit per treasure, with the index within the class at 0xE223. Entering a treasure scene, 0xAAFF checks that bit and, if it is set, the treasure never appears again.
You go down through the pits, and also by the ladder in scenes of kinds 0 and
one of those and that the player's X falls between 0x70 and 0x88 (0x83D4). That window is wider than the drawing: the mast drawn by 0x8F06 runs from 0x80 to 0x87, so you also go down from a little before stepping on it.
Down there the world runs at triple speed: bit 0 of 0xE2EB says whether you are on the surface —0xACE4 sets it at the start, 0x8751 clears it when you fall down a pit, 0x849A sets it on the way out— and with it clear, crossing a screen steps the register three places instead of one (0x9CD2).
With those two rules the shortest route that collects the 32 treasures can be computed: 189 screens crossed, against 238 never going down —21 % fewer—. It does not all go the same way: right until the first treasure, an about-turn, and the other 31 swept leftwards. It is a count of screens crossed, not a recorded game: ladders are counted as free and the clock is not in it.
Of the ten collision classes only four cost a life: 3 and 4 through 0x83B9, 6 and 9 through 0x8226 —the only two callers of the lose-a-life routine—. The rest:
The creatures the scenes set up, identified in the captures:
| routine | what it is | box |
|---|---|---|
| 0xAA74 | the snake | class 6, kills |
| 0xAAB7 | the campfire | class 6, kills |
| 0xAD1F | the standing log (the rolling ones come from its template) | class 1 |
| 0xA69E | the underground scorpion: it walks towards your X | class 9, kills |
You start with two spare lives (0x8A52), visible in two ways: three tiles on rows 2 and 3, and the colour of sprites 12 and 13, set to zero —transparent— when that life is spent (0x89A8).
Losing one does not repaint the scene: everything else is hidden, saving how many objects there were at 0xE189, the player is redrawn piece by piece, falls to the ground, and the objects are given back (0x8221-0x82E7). You reappear at the left edge, X 0x20 (0x826A).
The clock starts at 20:00 and counts down. It is not stored as a number: the five bytes at 0xE1D0 are already tile numbers —BA B8 C2 B8 B8, the drawings of “2”, “0”, “:”, “0”, “0”— and the countdown works on them (0x9DB8). When the borrow reaches the tens of minutes, time is up (0x9DEA): the clock stays at 00:00 and the ending sequence starts.
A tick takes 60 frames (0xE1D5), and the interrupt hook calls the clock once per interrupt with no condition on the way: one tick is 60 interrupts. Measured in a real game (tools/omsx_mide_tick.tcl): 55 ticks in a row, all 55 at exactly 60 interrupts. At 60 Hz the 20:00 last twenty wall-clock minutes; at 50 Hz, twenty-four: the cartridge counts interrupts, not seconds. The routine also runs on the title and the demo, over uninitialised tiles; the 20:00 are written when a real game starts. It does not run while paused.
The score is six binary digits at 0xE1D6-0xE1DB, turned into tiles when drawn at row 1, column 6 (0x9D72). Leading zeros are drawn blank until the first non-zero digit (0x9D5C). A treasure adds to the thousands digit (0x9D9F); subtracting points is 0x9D7C, told which digit to touch.
Four directions and one fire, from joystick or keyboard: the space bar and the cursors are remapped onto the same bits (0xB26E). Directions in bits 0-3 of 0xE05F, both fire buttons in bits 4 and 5 (0x87E0).
Holding the button does not jump again (0x87E9), and the only way off the vine is pressing down (0x81A7).
Three more keys, read from keyboard row 7 (0x9BF3):
| ESC | pause, with a press-release state machine at 0xE267 |
| RETURN | back to the title, only if 0xE269 allows it |
| STOP | starts from scratch, jumping to INIT |
The pause: 0x9C94 saves how many objects there were and writes zero. With the object list empty nothing moves, without a single if spread through the code. With one live object you cannot pause: that is the ending sequence.
0x9B6D keeps three cascaded counters (0xE25A/B/C, 60 each). Input reloads the outer two (0x9B74); with all three spent, register 1 of the video chip is set to 0x82 and the screen goes dark (0x9B8D). The game sits in a wait loop with interrupts disabled (di at 0x9B8C). Any direction or button wakes it (0x9B99) and, through keyboard row 7, RETURN, STOP or ESC (0x9BA9).
You do not leave the intro (0xB6B1) with a key: you leave when the demo script has spent seven of its entries (0xB751). With 0xE221 set to 1, the player's input is not read: every frame it is fed from the table at 0xB9E4, pairs of [how many frames][what is pressed] in the same format the keyboard produces (0xB9C8). The demo's game is six pairs plus three waits of 0xFF frames: eighteen bytes.
Two doors, and only two: running out of lives (0x8975, which on passing zero eats its own return address and gives the player handler 0x9E0E) or running out of clock (0x9DEA, through 0x9BCF). Both leave a single live object with the farewell handler: four sprites that come out and rise —Y is 0xBC minus the frame (0x9E8F)— over fourteen strips of drawing cycled in ten frames (0x9E67).
RETURN there jumps to 0x8065, where every game starts (0x9C91).