Raiders of the Lost Ark

[Keith Weisshar]

Why does Raiders of the Lost Ark return to normal after restart even after frying the game to the temple treasure room with corrupted graphics and then getting killed and ending the game with the pedestal fully raised and the Ark shown on the top of the screen and pressing the right controller button to restart. Game reset switch will not work after frying the game and I can only restart with the right controller button once the game ends.

Edited November 6, 2017 by Keith Weisshar

[Nukey Shay]

When you "fry" a game, you are essentially causing program execution to begin at a random place in the program...so pointers, variables, etc. have not been set up as they should have been. If you then begin a new game, some things may or may not return to normal (depending on how that program is written to do so). In Raiders, the program simply jumps back to the "cold start" address (the introductiory code in the cartridge which executes when you first power on the console), and all returns to normal. However, reading the Game Reset switch is disabled -if- Ram address $9C holds a positive value (0-127)...the program will branch right around checking it and the switch will do nothing. Until Ram address $9C holds a negative value (128-255), that is. It does this to allow the platform to move down before allowing Game Reset to happen immediately. In a "fried" state, Ram address $9C is holding the wrong value from the get-go.

[Keith Weisshar]

RAM address $9C is also used to determine whether the kernel should draw the Ark on the top of the Well of the Soul screen which only occurs if this address hold a positive value. The Ark is drawn at the start of a new game and disappears once the platform reaches the bottom of the pedestal and it is also drawn if I win the game by digging the correct mesa and finding the Ark. It does not draw at all if I lose the game by losing all three lives.

Edited November 8, 2017 by Keith Weisshar