     $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