     $FE67/65127:   Interrupt routine

    FE67: 48        PHA
    FE68: 8A        TXA
    FE69: 48        PHA             ; save registers
    FE6A: 98        TYA
    FE6B: 48        PHA
    FE6C: AD 0D 18  LDA $180D       ; interrupt from serial bus?
    FE6F: 29 02     AND #$02
    FE71: F0 03     BEQ $FE76       ; no
    FE73: 20 53 E8  JSR $E853       ; serve serial bus

    Jump from $FE71:

    FE76: AD 0D 1C  LDA $1C0D       ; interrupt from timer 1?
    FE79: 0A        ASL
    FE7A: 10 03     BPL $FE7F       ; no
    FE7C: 20 B0 F2  JSR $F2B0       ; IRQ routine for disk controller

    Jump from $FE7A:

    FE7F: 68        PLA
    FE80: A8        TAY
    FE81: 68        PLA             ; get registers back
    FE82: AA        TAX
    FE83: 68        PLA
    FE84: 40        RTI

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