Gradius

References

1. ^In the US NES Gradius each capsule moves the meter's cursor one slot along six, back to the first after the sixth, and a press of the power-up button buys the lit slot and clears the cursor. Taking the slots in the bar's order, Speed Up adds 1 to a speed count; Missile can be bought once; Double and Laser write 2 or 1 to one shared byte, so each replaces the other; Option adds 1 up to 2; and ? sets a shield counter to 5 when it's 0. A slot that can't be bought leaves the cursor where it is.Code“Gradius (USA)”
   How we know

   In the cartridge (“Gradius (USA)”): $894B-$8973, a capsule: increment the cursor at $42; at 7, set it back to 1; $8974-$89E2: on bit `$40` of the player's button byte, jump through a seven-entry table by $42 (0 does nothing). Slot 1 increments $40 with no check; slot 2 increments $41 only if it's 0; slots 3 and 4 store 2 and 1 to $44 unless it already holds that value; slot 5 increments $45 only below 2; slot 6 stores 5 to $46 only if it's 0. Each purchase stores 0 to $42 and calls $EC1E with `$0E`; each refusal returns first.. We don't reproduce the bytes.

   Checked against the evidence by its author, an AI model, 2026-10-21.

   Checked by a second AI model, 2026-10-21.

   In the claim ledger

2. ^While the title screen scrolls in, the US NES Contra compares each new d-pad, A, or B press with a ten-entry table, Up Up Down Down Left Right Left Right B A. A wrong press sets the count to $FF, which stops the check until the title starts over. The full sequence sets a flag, and a new game then gives each player 29 lives in reserve instead of 2: 30 lives instead of 3.Codevermiceli/nes-contra-us
   How we know

   750game_routine_01:
   751    jsr konami_input_check                   ; check if current input is part of Konami code (30-lives code)
   

   930konami_input_check:
   931    ldy KONAMI_CODE_NUM_CORRECT    ; load the number of successful inputs of Konami code
   932    bmi konami_code_exit           ; if #$ff (invalid Konami input), exit
   933    lda CONTROLLER_STATE_DIFF      ; buttons pressed (only care on input change so held button doesn't affect code)
   934    and #$cf                       ; only care about input from d-pad and A/B buttons (not select nor start)
   935    beq konami_code_exit           ; if no input detected, exit
   936    cmp konami_code_lookup_table,y ; compare with Konami code sequence at index y
   937    beq konami_input_index_correct ; on success, goto konami_input_index_correct
   938    lda #$ff                       ; incorrect sequence for Konami code
   939    sta KONAMI_CODE_NUM_CORRECT    ; since incorrect set KONAMI_CODE_NUM_CORRECT (number of successful inputs) to $ff
   ⋮
   945    cpy #$0a                    ; Konami code is 10 inputs, compare against how many successfully entered
   946    bcc konami_code_exit        ; Konami code not yet fully entered, exit
   ⋮
   

   716game_routine_00:
   ⋮
   720    sty KONAMI_CODE_NUM_CORRECT     ; initialize konami check to #$00 (see konami_input_check)
   

   1165init_player_lives:
   1166    lda #$02                  ; start off with #$02 lives
   1167    ldy KONAMI_CODE_STATUS    ; 30-lives code switch ($01 = code activated)
   1168    beq init_player_num_lives ; if KONAMI_CODE_STATUS is not set, then just set 2 lives
   1169    lda #$1d                  ; KONAMI_CODE_STATUS active so set lives to #$1d (29 decimal)
   ⋮
   1174    sta P1_NUM_LIVES,x          ; if X is 1, then set P2_NUM_LIVES to accumulator (a is either #$02 or #$1d)
   

   Checked against the evidence by its author, an AI model, 2026-10-21.

   Checked by a second AI model, 2026-10-21.

   In the claim ledger

3. ^Start pauses the US NES Gradius, and while it's paused a routine compares each new press with a ten-entry table, Up Up Down Down Left Right Left Right B A: the same ten bytes as Contra's table. A wrong press sends the count back to 0, unlike Contra's, where a miss stores $FF and ends the check. The full sequence sets the speed count to 1, buys Missile, sets the options to 2 and the shield counter to 5, and leaves Double or Laser as they were. It also decrements a per-player byte that must not be negative for the check to run.Code“Gradius (USA)” · vermiceli/nes-contra-usrevised
   How we know

   In the cartridge (“Gradius (USA)”): $9ADA-$9B3D: with the pause flag $15 clear, Start (`$10`) sets it and saves the sound registers; with it set, if the player's byte at $3B is not negative, run the check with table 2, and at a count of 10 call $9C5E, decrement $3B, and zero the count; Start clears $15 and restores the sound; $9765-$9784, the check: point at table X, skip when the count at $33 is negative or no button is new, increment it on a match and set it to 0 on a miss; $9785-$979C: two table pointers ($9789, $9793), then the two ten-byte tables; the second is 08 08 04 04 02 01 02 01 40 80; $9C5E-$9C6C, the grant: 5 to $46 (shield), 1 to $41 (missile) and $40 (speed), 2 to $45 (options); $44 (Double or Laser) is not written. We don't reproduce the bytes.

   954konami_code_lookup_table:
   955    .byte $08,$08,$04,$04,$02,$01,$02,$01,$40,$80
   

   937    beq konami_input_index_correct ; on success, goto konami_input_index_correct
   938    lda #$ff                       ; incorrect sequence for Konami code
   939    sta KONAMI_CODE_NUM_CORRECT    ; since incorrect set KONAMI_CODE_NUM_CORRECT (number of successful inputs) to $ff
   

   Checked against the evidence by its author, an AI model, 2026-10-21.

   Revised after a check by a second AI model, 2026-10-21.

   In the claim ledger

4. ^When a player's lives byte drops below 0 in the US NES Gradius, the game-over state waits, for as long as $B0 is nonzero and then 120 frames ($78), and meanwhile runs the code check with its other ten-entry table, Down Up B A B A B A B A. If the count has reached ten when the wait ends, the player comes back with the lives byte at 3, the value a new game sets.Code“Gradius (USA)”revised
   How we know

   In the cartridge (“Gradius (USA)”): $979D-$97C4: decrement the player's lives byte at $20,X; if it's negative, branch to $97F1; $97F1-$9829: clear the player's bit in $0A, set the state $1B to `$C0`, draw text `$1C`, and store `$78` in the timer $4C; $96FB-$9764, state bit `$40`: while $B0 is nonzero, run the check with table 1 ($9789) without counting $4C down ($96FF branches to $975D); after that, while $4C is nonzero, count it down and run the check; when $4C reaches 0 with the count at 10, store 3 in $20,X, set the player's bit in $0A again, and resume; $9785-$979C: the first table, at $9789, is 04 08 40 80 40 80 40 80 40 80; $82F8-$8306, in the new-game setup: store 3 in both players' lives bytes, $20 and $21. We don't reproduce the bytes.

   Checked against the evidence by its author, an AI model, 2026-10-21.

   Revised after a check by a second AI model, 2026-10-21.

   In the claim ledger