Bugs that Temptations has had since 1988. They are not disassembly mistakes: they are in the code exactly as it went on sale.
Each one comes with the code that produces it and, where it was possible, the check in the emulator. They go from least to most serious.
The routine that gives you an extra life:
DA_VIDA:
ld a,(08f12h) ; A = vidas actuales
inc a ; una mas
cp 00ah ; ¿ha llegado a 10?
ret z ; SI -> se va... SIN GUARDAR
ld (08f12h),a ; NO -> guarda el valor nuevo
call PINTA_MARCADOR
retThe ret z comes before the ld that stores. So if you have 9 lives and pick up another one, the inc a gives 10, the ret z fires, and the life is lost along the way.
You will never see 10 in the status bar. The real cap is 9.
It may be intentional — the status bar only has one digit, and the routine that draws it also clamps to 9 — but in that case the comparison would have to be with 10 and the order of the instructions the other way round. As it stands, the code says one thing and does another.
You can see this one just by playing.
When you pick up an item, the game has to erase it from the map. It does it like this:
BORRA_OBJETO_MAPA:
ld hl,07d80h ; SIEMPRE desde el principio del mapa
ld bc,00200h ; los 512 bytes de la pantalla
cpir ; busca el primer byte igual a A
...
ld (hl),000h ; y lo borracpir searches from the start of the buffer, not from where the player is. It finds the first tile of that type anywhere on the screen, whichever one it happens to be.
On a screen with a single item of each kind you don't notice. But:
| Screen | Repeated items |
|---|---|
| 16 | 2 ammo |
| 27 | 6 extra lives |
On screen 27, with six extra lives in plain sight, whichever one you pick up, the one that vanishes is always the first in scan order — top left. If you take the last one, you will see one on the other side of the screen disappear while the one you just touched is still drawn.
The routines that pick up items clear the tile before checking whether your counter is already at the cap. That is: if you pick up an extra life when you already have 9, or ammo when you are at the maximum, or the weapon you are already carrying, the item disappears from the map without giving you anything.
This is the most serious one, and it takes a while to show up.
The game sets up the stack only once, during startup:
GAME_START:
ld sp,0efffh ; pila provisional
...
ld sp,08fffh ; pila definitiva del juego <- 0x8058
jp INIT_PRINCIPALBut when you lose your last life, the game over ends like this:
call 08bfdh
jp 08076h ; reinicia... entrando DESPUES del ld sp0x8076 is the main initialisation, which is below the instruction that sets up the stack. So the new game starts with the stack pointer wherever the previous one left it.
Triggering eight game overs in a row and noting where the stack was left at each restart:
| Restart | Stack pointer |
|---|---|
| 1 | 0x8FFF |
| 2 | 0x8FFF |
| 3 | 0x8FFD |
| 4 | 0x8FFB |
| 5 | 0x8FF9 |
| 6 | 0x8FDB |
| 7 | 0x8FD9 |
| 8 | 0x8FD7 |
It goes down and never comes back up.
The stack grows downwards from 0x8FFF, and the game variables start at 0x8F00. So there are about 255 bytes of headroom: after enough lost games in a row without resetting the machine, the stack would end up writing over the game variables, with everything that implies.
In 1988, playing from a tape that took seven minutes to load, it was unlikely that anyone would string that many games together in one sitting. Today, with an emulator and instant loading, getting there is trivial.
Fix: change the destination of the jump from 0x8076 to an address that puts the stack back before carrying on.
When you finish the game, the victory screen goes into this loop:
BUCLE_FINAL:
call MUEVE_ENEMIGOS
halt
halt
halt
jp BUCLE_FINALIt doesn't read the keyboard. Not even CTRL+STOP works, because the game only checks that combination from the in-game routine, and that isn't called here.
Once the game is finished, the only way back is to reset the machine. It isn't exactly a bug — it may be deliberate, so that the final screen stays put — but it is worth knowing.
On screen 26 there is a hidden spot whose prize is a deadly tile.
Hidden spots are tiles that drop an item when you shoot them. Nearly all of them give ammo, weapons or lives. That one doesn't: it kills you.
It is in the data exactly like that, so it is intentional: a trap for anyone who goes around shooting at everything that moves. Very much in the spirit of a game that also keeps a telling-off for cheaters on the final screen.