$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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