Cheat code

References

1. ^ abStart 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

2. ^ abWhile 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. ^ abThe US NES Super C checks a different code from Contra's on its title screen: six presses, Right Left Down Up A B, against Contra's ten-press Up Up Down Down Left Right Left Right B A. Like Contra, a wrong press locks the check out. The code raises the starting lives byte from 2 to 9, where Contra's raises it from 2 to 29.Codevermiceli/nes-super-c · vermiceli/nes-contra-usrevised
   How we know

   539; checks for 10 extra lives cheat, i.e. right left down up a b
   540extra_lives_cheat_input_check:
   541    ldy EXTRA_LIVES_CHEAT_NUM_CORRECT ; load number of correct inputs to 10 extra lives cheat
   542    bmi @exit                         ; exit if failed inputting
   ⋮
   546    cmp extra_lives_code_tbl,y        ; compare input to next valid input for 10 lives cheat
   547    bne @mark_failure                 ; branch if incorrect to mark failure
   ⋮
   552    lda #$01
   553    sta CHEAT_CODE_STATUS             ; successfully entered full cheat code, mark success
   ⋮
   555@mark_failure:
   556    lda #$ff
   557    sta EXTRA_LIVES_CHEAT_NUM_CORRECT ; mark failure entering code
   ⋮
   564extra_lives_code_tbl:
   ⋮
   

   1154    jsr load_banks_extra_lives_cheat_input_check ; still animating intro, check for 10 extra lives cheat
   

   1504    lda #$02                           ; default to 3 lives
   1505    ldy CHEAT_CODE_STATUS              ; check if 10 lives cheat entered
   1506    beq @continue                      ; branch if not entered
   ⋮
   1510        lda #$09                       ; 10 lives cheat entered, set number of lives to 10
   ⋮
   1515    sta PLAYER_NUM_LIVES,x    ; set player number of lives
   

   930konami_input_check:
   ⋮
   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
   ⋮
   954konami_code_lookup_table:
   955    .byte $08,$08,$04,$04,$02,$01,$02,$01,$40,$80
   

   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)
   

   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