+------------------------------------------------------------------------
  |
  |      COMPLEX INTERFACE ADAPTER (CIA) 8520A (similar to CIA6526)
  |
  +------------------------------------------------------------------------
  |
  |   $4000/16384/CIA+0       Data Port Register A
  |   $4001/16385/CIA+1       Data Port Register B
  |   $4002/16386/CIA+2       Data Direction Register A
  |   $4003/16387/CIA+3       Data Direction Register B
  |   $4004/16388/CIA+4       Timer A: Low-Byte (Clock for FSM)
  |   $4005/16389/CIA+5       Timer A: High-Byte (Clock for FSM)
  |   $4006/16390/CIA+6       Timer B: Low-Byte (Interrupt Timer)
  |   $4007/16391/CIA+7       Timer B: High-Byte (Interrupt Timer)
  |   $4008/16392/CIA+8       Time-of-Day Clock: Low-Byte
  |   $4009/16393/CIA+9       Time-of-Day Clock: Middle-Byte
  |   $400A/16394/CIA+10      Time-of-Day Clock: High-Byte
  |   $400B/16395/CIA+11      Unused
  |   $400C/16396/CIA+12      Synchronous Serial I/O Data Buffer
  |   $400D/16397/CIA+13      CIA Interrupt Control Register
  |   $400E/16398/CIA+14      CIA Control Register A
  |   $400F/16399/CIA+15      CIA Control Register B
  |
  +------------------------------------------------------------------------