Platoon: discoveries

01 · Cheat

Secret: ZACH1 stops enemies and their bullets from killing the soldier

In the first section, holding Z, A, C, H and 1 together makes the main loop at $07B5 write rts over the first byte of $2BC8. That routine is the only test of whether the second figure has caught the soldier or a bullet in the enemy's shot slot has hit him, and with it gone neither can start his fall ($2CB7). Holding the five keys in the emulator changed $2BC8 from $EA to $60 (7 October 2026); N writes the $EA back.

The cheat does not cover everything that hurts him. A booby trap still springs and takes three hits ($39C1), walking on to the blown bridge still drops him into the river ($3D38), and the patrol still ends the game if the bridge stands ($35CB). The later sections, each a program of its own, carry no copy of the test.

02 · Quirk

A skill setting fixed at 2

The byte at $1EC6 is set to 2 when the game starts and never changed. With 2, the scroll moves two pixels a step instead of one ($B12A), enemies walk at 3 while the soldier walks the same way, and a jump while walking left holds 15 passes instead of 20. Unreached code at $1E80 once set it with F1 and F3, keys the finished game uses to switch men instead.

03 · Leftover

An ICON among the sprites

Sprite shape $A7, stored at $69C0 in the first section, is a filled block with the word ICON cut into it: an editor's placeholder that shipped with the game.

04 · Leftover

A game of Space Invaders inside the last section

The program for the last section carries a small, complete game of Space Invaders at $28E2 that nothing in Platoon starts. It draws three shields, puts four rows of six invaders at the top of the screen and a gun at the bottom, and takes over the screen's interrupts: the top row uses the play sprites, and three more interrupts ($0C1E, $0C60, $0CA2) reuse the sprites for the rows below, turning the border red, cyan and purple as they go.

The joystick moves the gun, and fire sends up one shot at a time ($2B17). The rows march sideways and step down at each edge, a little faster for every invader shot ($2BA9), while the invaders drop bombs in a fixed order of 25 turns ($2CD6) that wear the shields away ($2E4F). There is no score and there are no lives: a bomb on the gun, or the last invader shot, starts it all again ($2F0D).

The finished game still makes room for it. The panel's interrupt shows the gun and marks each frame for the invaders whenever the game's mode byte is 7 ($0E84), and only the invaders' own start sets that mode.

The hidden game running, entered by jumping to $28E2 from the middle of the jungle. Not every invader shows when it is started this way.