$180E/6158/VIA1+14:   Interrupt Enable Register

   +-------+------------------------------------------------------+
   | Bit 7 |   On Read:  Always 1                                 |
   |       |   On Write: 1 = Set Int.-Flags, 0 = Clear Int-.Flags |
   | Bit 6 |   Timer 1                                            |
   | Bit 5 |   Timer 2                                            |
   | Bit 4 |   CB1                                                |
   | Bit 3 |   CB2                                                |
   | Bit 2 |   Shift Register                                     |
   | Bit 1 |   CA1                                                |
   | Bit 0 |   CA2                                                |
   +-------+------------------------------------------------------+

ROM-Reference:

 STA $180E  : $EB37