Losing a life and starting again, the way Mario does

The walkers’ level with three lives. Play it and walk into a walker: the round stops, the square hops and falls, a screen says how many lives are left, and the level begins again. Lose all three to see the end. The program is 566 instructions in 1,456 bytes, built and checked the same way.

Play it here Change it on the desk The cartridge, to play anywhere that plays NES cartridges: lives.nes

On the screen

A life lost is a short scene of its own

When Mario touches a Goomba in Super Mario Bros., the game does not go straight to the next try. Everything stops, and Mario stays frozen where he was touched for a moment. Then he hops up and falls straight down off the screen, through the ground as if it were not there. Only when the fall is over is the life taken. The picture is then cleared for a plain screen showing the lives left, and after a while the level starts again from its beginning. This cartridge plays the same scene with its own timings, a smaller hop and its own words.

As written

The part of the program this lesson is about. The whole program is a plain text file: lives.s

;; The square and each walker: closer than 14 pixels across and 14 up
;; and down (the walkers stand on the ground, their top at 192) is a touch,
;; and the round stops there: the square hangs for 20 frames with the hop
;; already in it, 4 pixels a frame upward.
touch:
    LDX #$01
near:
    LDA $11
    SEC
    SBC $40,X
    BCS across1
    EOR #$FF
    ADC #$01
across1:
    CMP #$0E
    BCS apart
    LDA $15
    SEC
    SBC #$C0
    BCS down1
    EOR #$FF
    ADC #$01
down1:
    CMP #$0E
    BCS apart
    LDA #$01
    STA $50
    LDA #$14
    STA $51
    LDA #$00
    STA $16
    LDA #$FC
    STA $17
    RTS
apart:
    DEX
    BPL near
    RTS
;; The fall: the speed moves the square and pulls 96/256 a frame, up to 4
;; pixels a frame, through anything. Past the bottom of the screen a life
;; is taken and the screen for what is left comes up.
drop:
    CLC
    LDA $14
    ADC $16
    STA $14
    LDA $15
    ADC $17
    STA $15
    CLC
    LDA $16
    ADC #$60
    STA $16
    LDA $17
    ADC #$00
    STA $17
    BMI dropping
    CMP #$04
    BCC low
    LDA #$00
    STA $16
    LDA #$04
    STA $17
low:
    LDA $15
    CMP #$F0
    BCC dropping
    DEC $52
    JSR lives
dropping:
    RTS
;; The screen between rounds, drawn with the picture off: both tables
;; empty, every sprite out of sight, and a line of words in the middle,
;; LIVES and the count, or GAME OVER with none left; it stays 120 frames.
lives:
    LDA #$00
    STA $2001
    LDA #$20
    STA $2006
    LDA #$00
    STA $2006
    TAX
    LDY #$04
wipe2:
    STA $2007
    INX
    BNE wipe2
    DEY
    BNE wipe2
    LDA #$FF
hide2:
    STA $0200,X
    INX
    BNE hide2
    LDA #$21
    STA $2006
    LDA #$CC
    STA $2006
    LDA $52
    BEQ gameover
    LDX #$00
word1:
    LDA livesword,X
    STA $2007
    INX
    CPX #$06
    BNE word1
    LDA $52
    CLC
    ADC #$2A
    STA $2007
    LDA #$03
    STA $50
    JMP shown
gameover:
    LDX #$00
word2:
    LDA overword,X
    STA $2007
    INX
    CPX #$09
    BNE word2
    LDA #$04
    STA $50
shown:
    LDA #$78
    STA $51
    LDA #$00
    STA $2005
    STA $2005
    LDA #$1E
    STA $2001
    RTS

Before this one: A pause that holds the world still, the way Mario's does

Next: An item screen the picture slides away to show, the way Zelda's does

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