start disassembly of LIFE
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nino-porcino
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272601bc18
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; LIFE FOR APPLE-1
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; UNKNOWN AUTHOR
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; DISASSEMBLED BY ANTONINO PORCINO, 14TH SEP 2022
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ECHO = $FFEF ; character echo routine in woz monitor
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KEY_DATA = $D010 ; read key
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KEY_CTRL = $D011 ; control port
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DSP_DATA = $D012 ; write ascii
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DSP_CTRL = $D013 ; control port
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; zero page variables
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PTR1 = $F0 ; $F0-$F1
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PTR2 = $F2 ; $F2-$F3
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PTR3 = $F6 ; $F6-$F7
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PTR4 = $F8 ; $F8-$F9
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CELLCOUNT = $F9 ; also PTR4 high byte
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RND = $FA ; $FA-$FB random seed
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; board geometry is 40x24 = 960 bytes
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; primary board: $2440-$27FF
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; secondary board: $2840-$2BFF
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ROW0 = $2440
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ROW1 = $2468
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ROW22 = $27B0
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ROW23 = $27D8
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DEADCELL = $A0 ; " " (space character)
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ALIVECELL = $AA ; "*"
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FRAMECELL = $AD ; "-"
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ORG $2000
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;
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; quickly resets the primary board ($2400-$27FF)
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;
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LDX #$00
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LDA #DEADCELL ; dead cell character
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L2004 STA $2400,X ; bug: this should be $2440
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STA $2500,X
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STA $2600,X
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STA $2700,X
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INX
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BNE L2004
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;
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; prints welcome message (56 characters)
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; X is zero from previous BNE
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L2013 LDA MESSAGE,X
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JSR ECHO
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INX
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CPX #$38 ; prints 56 chars
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BNE L2013
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; read and print string from keyboard until ENTER is pressed
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; string is simply discarded, the purpose is to increment the
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; random seed in $FA-RND+1
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L201E JSR RDKEY
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CMP #$8D ; enter key
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BNE L201E
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;
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; fills the board with a random number of cells (from 32 to 95)
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; bug: also fills out of screen area between $2400 and $243F
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;
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JSR GETRAND ; gets a random number
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AND #$3F ; ranges it $00-$3F
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ADC #$20 ; ranges it $20-$5F (TODO: why carry is not cleared?)
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STA CELLCOUNT ; number of cells to write betwen $20-$5F (32-95)
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LDY #$00
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L2030 JSR GETRAND ; gets a random number
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AND #$03 ; ranges it 0-3
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CLC
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ADC #$24
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STA PTR1+1 ; high byte ranges from $24-$27
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LDA RND
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STA PTR1 ; PTR1 points randomly $2400-$27FF
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LDA #ALIVECELL ; alive cell character ("*")
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STA (PTR1),Y ; set cell "ON"
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DEC CELLCOUNT ; decrement cell count
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BNE L2030 ; loop until all cells are written
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;$2046
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; main game loop
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MAINLOOP LDA #$24
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STA PTR4+1
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LDA #$40
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STA PTR4 ; PTR4 = $2440
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;
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; marks top and bottom lines of the board to avoid out of bound checks
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;
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LDX #$27 ; $27=39, counts 40 characters backward
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LDA #FRAMECELL ; $AD = board limit character ("-")
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L2052 STA $27D8,X ; write bottom line of the board
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STA $2440,X ; write top line of the board
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DEX ; decrement 40 charc counter
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BPL L2052 ; loop if X >= 0
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; loop that prints the whole board from $2440 to $2800
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L205B LDA (PTR4),Y
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JSR ECHO
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INC PTR4
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BNE L205B
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INC PTR4+1
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LDA PTR4+1
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CMP #$28
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BNE L205B
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; reads the keyboard between each screen printout
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JSR RDKEY
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; copy true board into "working" board (copies $2440-$2800 into $2840-...)
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LDY #$00
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JSR SETPTRS ; PTR1=$2440, PTR2=$2840
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L2074 LDA (PTR1),Y
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STA (PTR2),Y
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INC PTR1
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INC PTR2
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BNE L2074
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INC PTR1+1
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INC PTR2+1
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LDA PTR1+1
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CMP #$28
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BNE L2074
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JSR ZEROBOARD ; fills the primary board all with zeros
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;
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; scans the secondary board does some computation and writes on the primary board
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;
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L208B LDY #$00
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LDA (PTR2),Y
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CMP #ALIVECELL ; is cell alive?
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BNE L209D ; if no go next cell
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LDY #$27 ; yes it's alive
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JSR L2114 ; ??
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LDY #$01
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JSR L211D ; ??
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; increment PTR1 and PTR2 to next cell
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L209D INC PTR1
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INC PTR2
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BNE L208B
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INC PTR1+1
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INC PTR2+1
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LDA PTR1+1
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CMP #$28 ; check end of the board
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BNE L208B
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;
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; ??? does something with top and bottom rows of the board
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; ROW1 = ROW1 + ROW23
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; ROW22 = ROW22 + ROW0
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; why??
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;
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CLC
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LDX #$27 ; count 40 characters (1 row)
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L20B0 LDA ROW23,X
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ADC ROW1,X
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STA ROW1,X
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LDA ROW0,X
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ADC ROW22,X
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STA ROW22,X
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DEX
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BPL L20B0
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JSR SETPTRS
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L20C8 LDY #$00
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LDA (PTR1),Y
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CMP #$02 ; ? two cells around
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BNE L20D4
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LDA (PTR2),Y
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BNE L20DE
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L20D4 CMP #$03 ; ? three cells around
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BNE L20DC
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LDA #ALIVECELL ; set next cell alive
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BNE L20DE
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L20DC LDA #DEADCELL ; set next cell dead
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L20DE STA (PTR1),Y
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INC PTR1
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INC PTR2
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BNE L20C8
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INC PTR1+1
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INC PTR2+1
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LDA PTR2+1
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CMP #$2C
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BNE L20C8
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JMP MAINLOOP
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; set pointers to:
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; PTR1 = $2440
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; PTR2 = $2840
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; $20F3
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SETPTRS LDA #$24
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STA PTR1+1
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LDA #$28
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STA PTR2+1
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LDA #$40
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STA PTR1
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STA PTR2
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RTS
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; $2102
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; reads a key and displays it on the terminal
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; returns key in A
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; increments a time counter $FA-$FB
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;
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RDKEY INC RND
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BNE L2108
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INC RND+1
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L2108 LDA KEY_CTRL
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BPL RDKEY
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LDA KEY_DATA
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JSR ECHO
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RTS
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; ???
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L2114 JSR L211D
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INY
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CPY #$2A
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BNE L2114
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RTS
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L211D ; increment cell at (PTR1),Y
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CLC
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LDA (PTR1),Y
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ADC #$01
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STA (PTR1),Y
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STY CELLCOUNT ; save Y into CELLCOUNT
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; PTR3 = PTR1 - Y
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SEC
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LDA PTR1
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SBC CELLCOUNT
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STA PTR3
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LDA PTR1+1
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SBC #$00
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STA PTR3+1
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; increment cell at (PTR3),Y e.g. (PTR1),-Y
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LDY #$00
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LDA (PTR3),Y
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CLC
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ADC #$01
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STA (PTR3),Y
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LDY CELLCOUNT ; restores Y
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RTS
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;
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;$213F
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; (possibly) advances the random number generator
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; and loads a random number into A
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; uses PTR3 as temporary variable?
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GETRAND LDA RND+1
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STA PTR3
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LDA RND
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ASL A
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ROL PTR3
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ASL A
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ROL PTR3
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CLC
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ADC RND
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PHA
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LDA PTR3
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ADC RND+1
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STA RND+1
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PLA
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ADC #$11
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STA RND
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LDA RND+1
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ADC #$36
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STA RND+1
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RTS
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;$2161
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;fills the primary board ($2440-$27FF) all with $00
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ZEROBOARD JSR SETPTRS
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LDA #$00
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TAY
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L2167 STA (PTR1),Y
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INC PTR1
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BNE L2167
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INC PTR1+1
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LDX PTR1+1
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CPX #$28 ; check end of the board
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BNE L2167
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JSR SETPTRS ; reset correct pointers on exit
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RTS
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L2179:
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DB A0 ; unused byte
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; $2180
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MESSAGE:
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DB $A0,$A0,$A0,$A0,$A0,$A0,$8D,$8D
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DB $8D,$8D,$C3,$CF,$CE,$D7,$C1,$D9
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DB $A7,$D3,$A0,$C7,$C1,$CD,$C5,$A0
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DB $CF,$C6,$A0,$CC,$C9,$C6,$C5,$8D
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DB $8D,$D0,$CC,$C5,$C1,$D3,$C5,$A0
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DB $D4,$D9,$D0,$C5,$A0,$D9,$CF,$D5
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DB $D2,$A0,$C6,$D5,$CC,$CC,$A0,$CE
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DB $C1,$CD,$C5,$AE,$8D,$8D,$00
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// $21B9
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