mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
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9b12b6fd9b
- getting ready for major changes for 0.6.0. - be sure to download the 0.5.0 release to ensure proper functionality, as these rountines will not work together in the SRC or BIN folder during the transition - Beginning to significantly alter documentation
77 lines
2.4 KiB
NASM
77 lines
2.4 KiB
NASM
*``````````````````````````````*
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* LRGPCLR (NATHAN RIGGS) *
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* *
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* FILLS THE LORES SCREEN WITH *
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* THE SPECIFIED COLOR. *
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* *
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* INPUT: *
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* *
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* .A = BACKGROUND COLOR *
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* *
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* OUTPUT: *
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* *
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* NONE *
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* *
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* DESTROY: AXYNVBDIZCMS *
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* ^^^^^ ^^^ *
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* *
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* CYCLES: 74 *
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* SIZE: 49 BYTES *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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]C EQU VARTAB ; TEMPORARY COLOR STORAGE
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*
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LRGPCLR
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STA ]C ; STORE COLOR
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ASL ; SHIFT LOW BYTE OF COLOR
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ASL ; INTO THE HIGH BYTE, SINCE
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ASL ; THE HIGH BYTE IS ALWAYS 0
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ASL
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CLC ; CLEAR CARRY
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ADC ]C ; NOW ADD LOW BYTE TO THE NEW HIGH
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STA ]C ; SO THAT IT IS A REPEATING NIBBLE
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LDY #$78 ; BYTE LENGTH FOR EACH LINE
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; THIS ALLOWS FOR FILLING EVERY PIXEL
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*
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LDX LWP ; CHECK WHICH PAGE TO CLEAR
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CPX #2 ; IS IT PAGE 2?
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BEQ :P2 ; IF SO, CLEAR PAGE 2
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; PTHERWISE, ASSUME PAGE 1
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*
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:LP1
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STA $400,Y ; PLOT FIRST SECTION
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STA $480,Y ; PLOT SECOND
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STA $500,Y ; THIRD
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STA $580,Y ; FOURTH
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CPY #80
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BPL :NDB
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STA $600,Y ; FIFTH
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STA $680,Y ; SIXTH
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STA $700,Y ; SEVENTH
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STA $780,Y ; EIGHTH
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:NDB
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DEY ; DECREASE OFFSET COUNTER
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BPL :LP1 ; IF NOT NEGATIVE, KEEP LOOPING
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JMP :EXIT
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*
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:P2
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*_PRN "PAGE 2"
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LDA ]C
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LDY #$78
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:LP2
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STA $800,Y ; PLOT FIRST SECTION
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STA $880,Y ; PLOT SECOND
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STA $900,Y ; THIRD
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STA $980,Y ; FOURTH
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CPY #80
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BPL :NDB2
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STA $0A00,Y ; FIFTH
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STA $0A80,Y ; SIXTH
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STA $0B00,Y ; SEVENTH
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STA $0B80,Y ; EIGHTH
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:NDB2
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DEY ; DECREASE OFFSET COUNTER
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BPL :LP2 ; IF NOT NEGATIVE, KEEP LOOPING
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:EXIT
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RTS
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