mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
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131 lines
3.5 KiB
Plaintext
131 lines
3.5 KiB
Plaintext
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*``````````````````````````````*
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* MEMFILL :: FILL MEMORY LOC *
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*- -*
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* FILLS A BLOCK OF MEMORY WITH *
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* THE SPECIFIED VALUE; USED *
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* OFTEN TO CLEAR LARGE BLOCKS. *
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*- -*
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* CLOBBERS: *
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* *
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* FLAGS: ????---- REG: AXYM *
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*- -*
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* CYCLES: ??? *
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* SIZE: *
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*- -*
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* USAGE: *
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* *
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* LDA #>$6A00 *
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* PHA *
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* LDA #<$6A00 *
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* PHA *
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* LDA #>1024 *
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* PHA *
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* LDA #<1024 *
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* PHA *
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* LDA #0 *
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* PHA *
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* JSR MEMFILL *
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*- -*
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* ENTRY *
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* *
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* TOP OF STACK *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HI BYTE OF RETURN ADDRESS *
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* FILL VALUE FOR MEMORY *
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* ARRAY SIZE *
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* LOW BYTE OF STARTING POINT *
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* HIGH BYTE OF STARTING POINT *
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*- -*
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* EXIT *
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* *
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* TOP OF STACK *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HI BYTE OF RETURN ADDRESS *
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* *
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* Y = COUNTER; TRASH *
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* X = COUNTER; TRASH *
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* A = LOW BYTE OF RET ADDR *
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*- -*
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* ADAPTED FROM LEVANTHAL AND *
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* WINTHROP'S /6502 ASSEMBLY *
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* LANGUAGE ROUTINES/. *
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* AS SUCH, THIS MAY NOT FALL *
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* UNDER THE APACHE 2.0 LICENSE *
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* AGREEMENT, SINCE THE BOOK *
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* WAS WRITTEN BEFORE THE *
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* LICENSE! *
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* *
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* THAT SAID, LEVENTHAL WROTE *
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* THAT THE PURPOSE OF THE BOOK *
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* WAS TO COPY THE SOURCE CODE, *
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* AS REINVENTING THE WHEEL IS *
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* TEDIOUS, AND HE PLACED NO *
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* RESTRICTIONS ON ITS USE. *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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MEMFILL
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*
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** SAVE RETURN ADDRESS
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*
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PLA
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STA :RETADR
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PLA
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STA :RETADR+1
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*
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** GET PARAMETERS
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*
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PLA
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STA :VALUE
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PLA
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STA :ARYSZ
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PLA
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STA :ARYSZ+1
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PLA
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STA ADDR1 ; ZERO PAGE POINTER
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PLA ; DEFINED IN
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STA ADDR1+1 ; DECS
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*
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** FILL WHOLE PAGES FIRST
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*
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LDA :VALUE ; GET VAL FOR FILL
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LDX :ARYSZ+1 ; X=# OF PAGES TO DO
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BEQ :PARTPG ; BRANCH IF HIGHBYTE OF SZ = 0
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LDY #0
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:FULLPG
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STA (ADDR1),Y
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INY ; INC TO NEXT BYTE
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BNE :FULLPG ; BRANCH IF NOT DONE W/ PAGE
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INC ADDR1+1 ; ADVANCE TO NEXT PAGE
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DEX
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BNE :FULLPG ; BRANCH IF NOT DONE W/ PAGES
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*
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** DO THE REMAINING PARTIAL PAGE
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** REGISTER A STILL CONTAINS VALUE
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*
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:PARTPG
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LDX :ARYSZ ;GET # OF BYTES IN FINAL PAGE
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BEQ :EXIT ; BRANCH IF LOW BYTE = 0
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LDY #0
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:PARTLP
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STA (ADDR1),Y ; STORE VAL
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INY ; INCREMENT INDEX
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DEX ; DECREMENT COUNTER
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BNE :PARTLP ; BRANCH IF NOT DONE
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:EXIT
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*
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** RESTORE RETURN ADDRESS
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*
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LDA :RETADR+1
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PHA
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LDA :RETADR
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PHA
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RTS
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*
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** DATA
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*
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:VALUE DS 1 ; FILL VALUE
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:ARYSZ DS 2 ; ARRAY SIZE
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:RETADR DS 2
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