$400D/16397/CIA+13:      CIA Interrupt Control Register

   +-------+------------------------------------------------------+
   | Bit 7 |   On Read:  1 = Interrupt occured                    |
   |       |   On Write: 1 = Set Int.-Flags, 0 = Clear Int-.Flags |
   | Bit 4 |   FLAG1 IRQ (ATN occured)                            |
   | Bit 3 |   Serial Port IRQ ($4C0C (FSM) is ready)             |
   | Bit 2 |   Time-of-Day Clock Alarm Interrupt                  |
   | Bit 1 |   Timer B Interrupt (Interrupt Timer)                |
   | Bit 0 |   Timer A Interrupt                                  |
   +-------+------------------------------------------------------+

   Standard-Wert: $9A/154 (%10011010)

   Your CIA does NOT clear this register! You have to do this by
   simply reading it.

ROM-Reference:

 BIT $400D  : $AADC $AAE9 $ACB1 $AD26 $ADC3 $ADD0 $AE42 $BA5B $BB92 $BB9F
              $BC44 $BC51 $BFA5
 LDA $400D  : $AE8D $DB02
 STA $400D  : $AF4B