mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-12-03 18:49:28 +00:00
84 lines
2.4 KiB
NASM
84 lines
2.4 KiB
NASM
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*``````````````````````````````*
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* HEX2BINASC (NATHAN RIGGS) *
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* *
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* INPUT: *
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* *
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* BPAR1 = HEX BYTE TO CONVERT *
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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: 134+ *
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* SIZE: 159 BYTES *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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]BINTAB ASC "0000" ; 0
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ASC "0001" ; 1
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ASC "0010" ; 2
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ASC "0011" ; 3
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ASC "0100" ; 4
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ASC "0101" ; 5
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ASC "0110" ; 6
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ASC "0111" ; 7
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ASC "1000" ; 8
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ASC "1001" ; 9
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ASC "1010" ; A
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ASC "1011" ; B
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ASC "1100" ; C
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ASC "1101" ; D
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ASC "1110" ; E
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ASC "1111" ; F
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*
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]LEFT EQU VARTAB ; LEFT NIBBLE
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]RIGHT EQU VARTAB+2 ; RIGHT NIBBLE
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]HBYTE EQU BPAR1 ; HEX BYTE
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*
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HEX2BINASC
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*
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LDA ]HBYTE
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AND #$F0 ; FIRST, MASK THE RIGHT NIBBLE
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LSR ; SHIFT RIGHT
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LSR ; SHIFT RIGHT
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LSR ; SHIFT RIGHT
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LSR ; SHIFT RIGHT
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STA ]LEFT ; STORE AS LEFT NIBBLE
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LDA ]HBYTE
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AND #$0F ; NOW MASK LEFT NIBBLE
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STA ]RIGHT ; STORE AS RIGHT NIBBLE
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*
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** GET LEFT FROM LOOKUP TABLE
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*
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ASL ]LEFT ; MULTIPLY ]LEFT NIBBLE
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ASL ]LEFT ; BY FOUR
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LDX ]LEFT ; TO GET LOOKUP TABLE OFFSET
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LDA ]BINTAB,X ; TRANSFER APPROPRIATE
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STA RETURN ; PART OF THE TABLE TO RETURN
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LDA ]BINTAB,X+1
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STA RETURN+1
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LDA ]BINTAB,X+2
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STA RETURN+2
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LDA ]BINTAB,X+3
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STA RETURN+3
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*
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** NOW GET RIGHT
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*
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ASL ]RIGHT ; MULTIPLY ]RIGHT BY 4
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ASL ]RIGHT ; TO GET LOOKUP TABLE OFFSET
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LDX ]RIGHT
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LDA ]BINTAB,X ; AND TRANSFER APPROPRIATE
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STA RETURN+4 ; STRING TO RETURN AFTER
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LDA ]BINTAB,X+1 ; THE PREVIOUS NIBBLE
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STA RETURN+5
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LDA ]BINTAB,X+2
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STA RETURN+6
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LDA ]BINTAB,X+3
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STA RETURN+7
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*
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LDA #8 ; LENGTH IN .A AND RETLEN
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STA RETLEN
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RTS
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