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77 lines
4.1 KiB
Plaintext
77 lines
4.1 KiB
Plaintext
;Atari 2600 Two Player Score Kernel
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;Score Routine Variables
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SCORE0 EQU $E8 ;Player One Score
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SCORE1 EQU $E9 ;Player Two Score
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SC0ONE EQU $EA ;One Score Ones Digit Offset
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SC1ONE EQU $EB ;Player Ten Score Ones Digit Offset
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SC0TEN EQU $EC ;Player One Score Ones Digit Offset
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SC1TEN EQU $ED ;Player Ten Score Ones Digit Offset
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SC0GFX EQU $EE ;Player One Score Graphics Data
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SC1GFX EQU $EF ;Player Two Score Graphics Data
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;Prep Scores For Diplay
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SCPREP: LDX #1 ;Offset into SCORE0/SCORE1
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SCPREL: LDA SCORE0,X ;Get SCORE1 (First Pass) or SCORE0 (Second Pass)
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AND #$0F ;Remove Tens Digit
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STA TEMP0 ;And Save It
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ASL ;Multiply By 4
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ASL ;(Carry will be Clear because of AND/ASL)
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ADC TEMP0 ;Add To Original Value for Multiply by 5
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STA SC0ONE,X ;Store in SC0ONE (First Pass) or SC1ONE (Second Pass)
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LDA SCORE0,X ;Get SCORE1 (First Pass) or SCORE0 (Second Pass)
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AND #$F0 ;Remove Ones Digit
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LSR ;Divide by 4
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LSR ;
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STA TEMP0 ;And Save It
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LSR ;Divide by 4 Again
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LSR ;(Leaving Carry Clear)
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ADC TEMP0 ;Add Saved Value, Resulting in Digit / 16 * 5
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STA SC0TEN,X ;Store in SC0TEN (First Pass) or SC1TEN (Second Pass)
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DEX ;Point to SCORE 1
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BPL SCPREL ;AND Loop if >0
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RTS ;Return
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;scdisp() - Score Display Kernel - Uses 12 Scanlines Total
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SCDISP: LDA #2 ; - Use Player Colors
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STA CTRLPF ; - Set Playfield Control Register
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LDX #5 ; 43 - cycle after looping
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SCDISL: LDY SC0TEN ; 3 46 - get the tens digit offset for the Score
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LDA DGTGFX,Y ; 5 51 - use it to load the digit graphics
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AND #$F0 ; 2 53 - remove the graphics for the ones digit
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STA SC0GFX ; 3 56 - AND save it
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LDY SC0ONE ; 3 59 - get the ones digit offset for the Score
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LDA DGTGFX,Y ; 5 64 - use it to load the digit graphics
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AND #$0F ; 2 66 - remove the graphics for the tens digit
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ORA SC0GFX ; 3 69 - merge with the tens digit graphics
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STA SC0GFX ; 3 72 - AND save it
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STA WSYNC ; 3 75 - wait for end of scanline
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STA PF1 ; 3 3 - @66-28, update playfield for Score dislay
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LDY SC1TEN ; 3 6 - get the left digit offset for the Timer
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LDA DGTGFX,Y ; 5 11 - use it to load the digit graphics
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AND #$F0 ; 2 13 - remove the graphics for the ones digit
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STA SC1GFX ; 3 16 - AND save it
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LDY SC1ONE ; 3 19 - get the ones digit offset for the Timer
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LDA DGTGFX,Y ; 5 24 - use it to load the digit graphics
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AND #$0F ; 2 26 - remove the graphics for the tens digit
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ORA SC1GFX ; 3 29 - merge with the tens digit graphics
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STA SC1GFX ; 3 32 - AND save it
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JSR SCDISX ;12 44 - waste 12 cycles
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STA PF1 ; 3 47 - @39-54, update playfield for Timer display
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LDY SC0GFX ; 3 50 - preload for next scanline
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STA WSYNC ; 3 53 - wait for end of scanline
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STY PF1 ; 3 3 - @66-28, update playfield for the Score display
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INC SC0TEN ; 5 8 - advance for the next line of graphic data
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INC SC1TEN ; 5 13 - advance for the next line of graphic data
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INC SC0ONE ; 5 18 - advance for the next line of graphic data
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INC SC1ONE ; 5 23 - advance for the next line of graphic data
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JSR SCDISX ;12 35 - waste 12 cycles
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DEX ; 2 37 - decrease the loop counter
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STA PF1 ; 3 40 - @39-54, update playfield for the Timer display
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BNE SCDISL ; 2 42 - (3 43) if dex != 0 then branch to ScoreLoop
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STA WSYNC ; 3 45 - wait for end of scanline
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STX PF1 ; 3 3 - x = 0, so this blanks out playfield
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STA WSYNC ; 3 6 - wait for end of scanline
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SCDISX: RTS ; 6 12 - Return
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