29 lines
1000 B
Plaintext
29 lines
1000 B
Plaintext
;THIS SUBROUTINE MOVES A BLOCK OF DATA IN MEMORY. THE STARTING
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;ADDRESS OF THE DATA IS CONTAINED IN LOCATIONS $40 (LOW ADDRESS
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;BYTE) AND $41 (HIGH ADDRESS BYTE). THE STARTING ADDRESS OF
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;THE DESTINATION OF THE DATA IS CONTAINED IN LOCATIONS $42 (LOW
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;ADDRESS BYTE) AND $43 (HIGH ADDRESS BYTE). THE NUMBER OF BYTES
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;TO BE MOVED IS CONTAINED IN LOCATION $44.
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MOVE8 LDX $44 /LOAD BYTE COUNT INTO X REGISTER
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SEC /CALCULATE MOVE DISPLACEMENT
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LDA $42
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SBC $40
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LDA $43
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SBC $41
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BMI DISPN /DISPLACEMENT NEGATIVE?
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LDY $44 /NO. START MOVE WITH LAST BYTE
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CONTI DEY
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LDA ($40),Y /LOAD BYTE FROM SOURCE LOCATION
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STA ($42),Y / AND STORE IT AT DESTINATION LOCATION
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DEX /DECREMENT BYTE COUNT
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BNE CONTI /LOOP UNTIL ALL BYTES MOVED
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RTS
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DISPN LDY #00 /START MOVE WITH FIRST BYTE
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CONT2 LDA ($40),Y /LOAD BYTE FROM SOURCE LOCATION
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STA ($42),Y / AND STORE IT AT DESTINATION LOCATION
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INY /INDEX TO NEXT BYTE
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DEX /DECREMENT BYTE COUNT
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BNE CONT2 /LOOP UNTIL ALL BYTES MOVED
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RTS
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