6522 VIA
                                    ========

+---------+-----------------------------+-----------------------------+
|         |           Write             |            Read             |
+=========+=============================+=============================+
| base+0  | Output register B           | Input register B            |
| base+1  | Output register A           | Input register A            |
| base+2  | Data direction register B   | Data direction register B   |
| base+3  | Data direction register A   | Data direction register A   |
| base+4  | T1 low-order counter        | T1 low-order latches        |
| base+5  | T1 high-order counter       | T1 high-order counter       |
| base+6  | T1 low-order latches        | T1 low-order latches        |
| base+7  | T1 high-order latches       | -                           |
| base+8  | T2 low-order latches        | T2 low-order counter        |
| base+9  | T2 high order counter       | T2 high order counter       |
| base+10 | Shift register              | Shift register              |
| base+11 | Auxilary control register   | Auxilary control register   |
|         |  b7-b6=T1, b5=T2, b4-b2=SR, b1=PB latch, b0=PA latch      |
| base+12 | Peripheral control register | Peripheral control register |
|         |  b7-b3=CB2, b4=CB1, b3-b1=CA2, b0=CA1                     |
| base+13 | Interrupt flag register     | Interrupt flag register     |
| base+14 | Interrupt enable register   | Interrupt enable register   |
|         |  b7=clr/set, b6=T1, b5=T2, b4=CB1, b3=CB2                 |
|         |                     b2=SR, b1=CA1, b0=CA2                 |
| base+15 | Output A, no handshake      | Input A, no handshake       |
+=========+=============================+=============================+


Base  Device
------------------------------------------------------
FE40  BBC System VIA
FE60  BBC User VIA
FEF0  6522/8255 one-channel Tube port (CUBE, Torch)
B800  Atom System VIA