$DC0D/56333/CIA1+13: CIA Interrupt Control Register (IRQ) +-------+------------------------------------------------------+ | Bit 7 | IRQ Flag (1 = IRQ Occurred) / Set-Clear Flag | | Bit 4 | FLAG1 IRQ (Cassette Read / Serial Bus SRQ Input) | | Bit 3 | Serial Port Interrupt ($DC0C full/empty) | | Bit 2 | Time-of-Day Clock Alarm Interrupt | | Bit 1 | Timer B Interrupt | | Bit 0 | Timer A Interrupt | +-------+------------------------------------------------------+ Your CIA does NOT clear this register! You have to do this by simply reading it. Default Value: $81/129 (%10000001) Kernal-Reference: LDA $DC0D : $EA7E $ED9C $ED9F $EE2D $EE30 $F91A $F948 $FBB7 LDX $DC0D : $FB52 STA $DC0D : $F87A $FA3F $FA50 $FCA2 $FDA5 $FF70 STX $DC0D : $FB4F STY $DC0D : $F877