mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
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101 lines
2.4 KiB
Plaintext
101 lines
2.4 KiB
Plaintext
*
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*``````````````````````````````*
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* ADDIT16 :: ADD 16-BIT VALUES *
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*- -*
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* ADDS TWO SIXTEEN BIT VALUES *
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* AND RETURNS A 16 BIT VALUE *
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* IN .Y (LOW) AND .X (HIGH). *
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* CAN BE SIGNED OR UNSIGNED. *
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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 #>1000 *
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* PHA *
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* LDA #<1000 *
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* PHA *
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* LDA #>1200 ; ADD2 *
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* PHA *
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* LDA #<1200 *
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* PHA *
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* JSR ADDIT16 *
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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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* ADDEND 2 LOW BYTE *
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* ADDEND 2 HIGH BYTE *
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* ADDEND 1 LOW BYTE *
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* ADDEND 1 HIGH BYTE *
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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 = LOW BYTE OF RESULT *
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* .X = HIGH BYTE OF RESULT *
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* .A = LOW BYTE OF RET ADDR *
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* *
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* [RETURN] = RESULT (2 BYTES) *
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* [RETLEN] = 2 (RESULT LENGTH) *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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ADDIT16
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*
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** GET RETURN ADDR
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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 :ADD2
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PLA
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STA :ADD2+1
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PLA
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STA :ADD1
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PLA
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STA :ADD1+1
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*
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LDA :ADD1
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CLC
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ADC :ADD2
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TAY ; LOW BYTE
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STY RETURN
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LDA :ADD1+1
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ADC :ADD2+1
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TAX ; HIGH BYTE
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STX RETURN+1
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LDA #2
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STA RETLEN
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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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*
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RTS
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*
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** DATA
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*
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:ADD1 DS 2
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:ADD2 DS 2
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*
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