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83 lines
2.4 KiB
Plaintext
83 lines
2.4 KiB
Plaintext
; C02 Interrupt Vector Assembly Language Routines for VIC-20
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;getirq() - Return IRQ Interrupt Handler Address
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;Returns: A = $00 - Software Definable Address
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; Y = Address MSB
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; X = Address LSB
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GETIRQ: LDA #$00 ;Return software definable
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LDX $0314 ;and Address in CINV
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LDY $0315
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RTS
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;getbrk() - Return BRK Interrupt Handler Address
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;Returns: A = $00 - Software Definable Address
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; Y = Address MSB
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; X = Address LSB
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GETBRK: LDA #$00 ;Return software definable
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LDX $0316 ;and Address in CBINV
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LDY $0317
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RTS
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;getnmi() - Return NMI Interrupt Handler Address
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;Returns: A = $00 - Software Definable Address
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; Y = Address MSB
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; X = Address LSB
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GETNMI: LDA #$00 ;Return software definable
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LDX $0318 ;and Address in CBINV
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LDY $0319
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RTS
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;getrst() - Return RESET Interrupt Handler Address
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;Returns: A = $7F - Firmware Defined Address
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; Y = Address MSB
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; X = Address LSB
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GETRST: LDX $FFFC ;Load 6502 Interrupt Vector
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LDY $FFFD ;and Fall into SETRST
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;setrst() - Set RESET Interrupt Handler Address
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;Args: Y = Address MSB
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; X = Address LSB
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;Returns: A = $7F - Failure - Can't be Changed
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SETRST: LDA #$7F ;Return "Hard Coded"
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RTS
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;setirq() - Set IRQ Interrupt Handler Address
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;Args: Y = Address MSB
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; X = Address LSB
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;Returns: A = $00 - Successfully Set
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SETIRQ: SEI ;Disable Interrupts
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STX $0314 ;Store Address in CINV
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STY $0315
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CLI ;Enable Interrupts
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LDA #$00 ;Return "Modified"
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RTS
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;setrst() - Set BRK Interrupt Handler Address
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;Args: Y = Address MSB
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; X = Address LSB
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;Returns: A = $00 - Successfully Set
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SETBRK: SEI ;Disable Interrupts
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STX $0316 ;Store Address in CBINV
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STY $0317
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CLI ;Enable Interrupts
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LDA #$00 Return "Modified"
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RTS
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;setnmi() - Set NMI Interrupt Handler Address
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;Args: Y = Address MSB
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; X = Address LSB
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;Returns: A = $00 - Successfully Set
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SETNMI: STX $0318 ;Store Address in NMINV
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STY $0319
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LDA #$00 ;Return "Modified"
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RTS
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;xitirq - Exit from IRQ Interrupt
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;Exit IRQ if not Executing System IRQ Routine
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XITIRQ: PLA ;Restore Y Register
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TAY
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PLA ;Restore Y Register
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TAX
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PLA ;Restore Accumulator
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RTI ;Return from Interrupt
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