Donkey Kong Jr. (NES)

Donkey Kong Jr.
Developer: Nintendo R&D1 Publisher: Nintendo Platforms: NES, Famicom Disk System Released in JP: July 15, 1983 (Famicom), July 19, 1988 (FDS) Released in US: June 23, 1986 Released in EU: June 15, 1987 This game has unused code. This game has revisional differences.

Donkey Kong Jr. is the NES port of Donkey Kong's sequel which would later be adapted into an educational title.

Unused Enemy Behavior

Memory addresses 0x510-0x515 are meant to store parameters for enemy behavior based on the current difficulty level, but 0x513 is unused. Based on a section of unused code in Revision 0 at 0xDFAE, it appears that this would have been a way for the game to increase the chance that new enemy spawns move towards Jr. when he is close to the top of the stage. The normal rate at which this occurs is stored at 0x515, though it is set at a constant value of 0xB0 (68.75%) for all loops. This section of code is removed from Revision 1, though 0x513 still remains unused.

Revisional Differences

Revision 0 vs Revision 1

Title Screen

In Revision 0, holding Select on the title screen starts a 64 frame countdown, after which the game will begin automatically scrolling through the menu options. Memory address 0x6A keeps track of how many times it has advanced; once it loops back to 0x00, the countdown begins again. Revision 1 completely removes this function for some reason.

Controller Input

Similar to the original Revision 0 version of Donkey Kong, Jr. cannot move at all when the D-Pad is held diagonally. In the more common Revision 1 version, the controller reading code was improved so that the first direction pressed has priority: if the D-Pad is rolled from Up / Down to diagonal Jr. will not start walking, but if the D-Pad is rolled from Left / Right to diagonal he will not stop walking.

Stage 2 Glitch

In Revision 0, if the final vine of Stage 2 is grabbed from the left side, a glitched ending animation will occur: Jr. will climb down the vine instead of up, then appear on the final platform. This is in part due to the platform's hitbox jutting out too far to the right, preventing Jr. from climbing up normally. In Revision 1, the hitbox of this platform has been shortened by two pixels to prevent this from happening.

Palettes

Revision 1 features some palette changes:

In Revision 0, some of the fruit becomes lighter-colored while falling. In Revision 1, the corresponding palette has been edited so that they always retain the same colors.

Revision 0	Revision 1

In Stage 4, the chains have been brightened to help them stand out from the background.