Via Interrupt enable Reg $e

if bit 7 is 1
     0 interrupt disabled
     1 interrupt enabled

if bit 7 is 0
     1 interrupt disabled
     0 interrupt enabled

• 0x01 : bit 0 CA2 interrupt

• 0x02 : bit 1 CA1 interrupt

• 0x04 : bit 2 Shiftreg interrupt

• 0x08 : bit 3 CB2 interrupt

• 0x10 : bit 4 CB1 interrupt

• 0x20 : bit 5 Timer2 interrupt

• 0x40 : bit 6 Timer1 interrupt

• 0x80 : bit 7 indicates whether ANY interrupt happened