+------------------------------------------------------------------------
  |
  |      VERSATILE INTERFACE ADAPTER (VIA) 6522
  |
  +------------------------------------------------------------------------
  |
  |  Register description:
  |
  |  VIA 1 (Serial Bus):
  |
  |   $1800/6144/VIA1+0       Data Port B (ATN, CLOCK, DATA, Device #)
  |   $1801/6145/VIA1+1       Data Port A (free for parallel cables)
  |   $1802/6146/VIA1+2       Data Direction Register B
  |   $1803/6147/VIA1+3       Data Direction Register A
  |   $1804/6148/VIA1+4       Timer 1 Low-Byte (Timeout Errors)
  |   $1805/6149/VIA1+5       Timer 1 High-Byte (Timeout Errors)
  |   $1806/6150/VIA1+6       Timer 1-Latch Low-Byte (Timeout Errors)
  |   $1807/6151/VIA1+7       Timer 1-Latch High-Byte (Timeout Errors)
  |   $1808/6152/VIA1+8       Timer 2 Low-Byte (unused)
  |   $1809/6153/VIA1+9       Timer 2 High-Byte (unused)
  |   $180A/6154/VIA1+10      Shift Register
  |   $180B/6155/VIA1+11      Auxiliary Control Register
  |   $180C/6156/VIA1+12      Peripheral Control Register
  |   $180D/6157/VIA1+13      Interrupt Flag Register
  |   $180E/6158/VIA1+14      Interrupt Enable Register
  |   $180F/6159/VIA1+15      Data Port A* (no handshake)
  |
  |  VIA 2 (Motor and Head Control):
  |
  |   $1C00/7168/VIA2+0       Data Port B (SYNC, Motors, Bit Rates, LED)
  |   $1C01/7169/VIA2+1       Data Port A (Data to/from head)
  |   $1C02/7170/VIA2+2       Data Direction Register B
  |   $1C03/7171/VIA2+3       Data Direction Register A
  |   $1C04/7172/VIA2+4       Timer 1 Low-Byte (IRQ Timer)
  |   $1C05/7173/VIA2+5       Timer 1 High-Byte (IRQ Timer)
  |   $1C06/7174/VIA2+6       Timer 1-Latch Low-Byte (IRQ Timer)
  |   $1C07/7175/VIA2+7       Timer 1-Latch High-Byte (IRQ Timer)
  |   $1C08/7176/VIA2+8       Timer 2 Low-Byte (unused)
  |   $1C09/7177/VIA2+9       Timer 2 High-Byte (unused)
  |   $1C0A/7178/VIA2+10      Shift Register
  |   $1C0B/7179/VIA2+11      Auxiliary Control Register
  |   $1C0C/7180/VIA2+12      Peripheral Control Register
  |   $1C0D/7181/VIA2+13      Interrupt Flag Register
  |   $1C0E/7182/VIA2+14      Interrupt Enable Register
  |   $1C0F/7183/VIA2+15      Data Port A* (no handshake)
  |
  +------------------------------------------------------------------------

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