An 8 KB cartridge in page 1, from 0x4000 to 0x5FFF. It is the smallest Konami cartridge in this series — half of any of the others.
4000 41 42 b4 41 00 00 00 00 ... "AB", then INIT = 0x41B4Only INIT is declared; the other three vectors are zero. INIT hooks the interrupt by writing jp 0x4012 into H.KEYI (0xFD9A) one byte at a time, wipes the 2 KB of game RAM with a single LDIR, puts the stack at 0xE7FF and loads the title screen.
SCREEN 2, with the eight registers coming from 0x49A3:
| name table | 0x3800 |
| pattern table | 0x2000 |
| colour table | 0x0000 |
| sprite attributes | 0x3B00 |
| sprite patterns | 0x1800, 16×16 |
SCREEN 2 splits patterns and colours into three 2 KB thirds and the game wants them identical. It gets that with one copy of 4095 bytes whose destination runs 2 KB ahead of the source (0x471A): past the first third it is already reading what it just wrote, so the second propagates into the third by itself.
Twelve blocks with a header — destination, size, data — go up from 0x4B36 (0x4956 reads them). Then the same bytes go up a second time, at characters 0x98 and 0xB7, because in SCREEN 2 colour goes per pattern line and the same character cannot be two colours. The colour table gives cyan to one copy and white to the other.
The digits of the scoreboard are patterns 0xE0 to 0xE9, which is why printing a BCD number is just adding 0xE0 to the digit (0x4651).
Logs, turtles and cars are not sprites. They are characters, and to move them two pixels at a time the cartridge keeps four versions of every drawing in video memory, shifted 0, 2, 4 and 6 pixels (0x473C).
Each object's position is stored in quarters of a character: the low two bits pick the version and the rest is the column. Each row is assembled in a RAM buffer of two rows of 40 columns (0xE600) and 22 columns of it are then pushed to video memory.
Only four things use sprites: the frog (two), the crocodile (four), the creature that crosses the river and the frog you rescue. That is what the MSX1's limit of four sprites per line is being saved for.
Three channels, each with an 8-byte record (0xE020, 0xE028, 0xE030). A tune is a string of three-byte notes: fine period, coarse period with the volume in the top nibble and bit 3 for noise, and duration. A negative duration makes the note fade on its own. 0xFF ends the tune.
Priority is by address: 0x50E7 only takes a new effect if the channel is quiet or if the tune being asked for sits at a lower address than the one playing.
These 163 bytes are the same code as Time Pilot's — see Findings.
| bytes | ||
|---|---|---|
| traced code | 4,880 | 59.57 % |
| identified data | 3,312 | 40.43 % |
| unexplained | 0 | 0.00 % |