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https://github.com/nathanriggs/AppleIIAsm-Collection.git
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52 lines
2.0 KiB
NASM
52 lines
2.0 KiB
NASM
*``````````````````````````````*
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* HEXASC2HEX *
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* *
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* INPUT: *
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* *
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* ZPW1 = HEX STRING ADDRESS *
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* *
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* DESTROYS: NZCIDV *
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* ^^^ ^ *
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* *
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* CYCLES: 94+ *
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* SIZE: 56 BYTES *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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]HI EQU ZPW2 ; HIGH BYTE
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]LO EQU ZPW3 ; LOW BYTE
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]STR EQU ZPW1 ; ADDR OF STRING TO CONVERT
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*
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HEXASC2HEX
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LDY #1 ; {3C2B} GET FIRST HEX CHARACTER
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LDA (]STR),Y ; {6C2B}
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STA ]HI ; {4C3B} STORE IN HIBYTE
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INY ; {2C1B} INCREASE INDEX
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LDA (]STR),Y ; {6C2B} TO GET SECOND HEX CHARACTER
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STA ]LO ; {4C3B} AND STORE THAT IN LOW BYTE
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*
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SEC ; {2C1B} SET CARRY
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SBC #'0' ; {3C2B} SUBTRACT '0' CHAR FROM ]LO CHAR
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CMP #10 ; {3C2B} ASCII NUMERALS OFFSET
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BCC :CONT ; {3C2B} IF NUMERAL, CONTINUE
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SBC #7 ; {2C2B} OTHERWISE SUBTRACT LETTER OFFSET
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:CONT
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STA ]LO ; {4C3B} STORE VALUE INTO LOW BYTE
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LDA ]HI ; {4C3B} NO WORK ON HIGH BYTE
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SEC ; {2C1B} SET CARRY
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SBC #'0' ; {2C2B} SUBTRACT '0' ASCII
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CMP #10 ; {3C2B} IS NUMBER?
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BCC :C2 ; {3C2B} THEN DONE
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SBC #7 ; {2C2B} OTHERWISE LETTER OFFSET
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:C2
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STA ]HI ; {4C3B} STORE HIGH BYTE VALUE
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ASL ; {2C1B} CLEAR LOW BYTE OF ]HI
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ASL ; {2C1B}
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ASL ; {2C1B}
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ASL ; {2C1B}
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ORA ]LO ; {7C3B} OR OPERATION TO INSERT
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; LOW BYTE INTO RESULT
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LDY #1 ; {3C2B} SET LENGTH OF RETURN
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STY RETLEN ; {4C3B}
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STA RETURN ; {4C3B} PASS BACK VIA RETURN AND .A
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RTS ; {6C1B}
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