8279 Keyboard/Display Controller
                     ================================

+--------+---------------------------------+-------------------------------+
|        |              Write              |             Read              |
+========+=================================+===============================+
| base+0 |   Transmit Data Register        |    Receive Data Register      |
|        |                                 | Keyscan data:                 |
|        |                                 |  b7: Control                  |
|        |                                 |  b6: Shift                    |
|        |                                 |  b5-b3: Scan Row              |
|        |                                 |  b2-b0: Scan Column           |
+--------+---------------------------------+-------------------------------+
| base+1 |      Control Register           |       Status Register         |
|        |  b7-b5: Command                 |  b7: Display unavailable      |
|        |  b4-b0: Data                    |  b6: Error: Multiple keys     |
|        | Commands:                       |  b5: Error: Overrun           |
|        | 000DSKKE Keyboard/Display mode  |  b4: Error: Underrun          |
|        |    D     - direction left/right |  b3: FIF0 full                |
|        |     S    - size 8/16 characters |  b2-b0: Num. of chars in FIFO |
|        |        E - Enc/Decoded keyboard |                               |
|        |      00  - 2-key lockout        |                               |
|        |      01  - n-key rollover       |                               |
|        |      10  - Scan sensor matrix   |                               |
|        |      11  - Strobed input        |                               |
|        |                                 |                               |
|        | 001ppppp - Program clock        |                               |
|        | 010IxAAA - Read FIFO/Sensor RAM |                               |
|        | 011IAAAA - Read display RAM     |                               |
|        | 100IAAAA - Write display RAM    |                               |
|        |         I=AutoInc, AAAA=address |                               |
|        | 101xWWBB - Display inhibit/blank|                               |
|        | 110CCCCC - Clear                |                               |
|        | 111Exxxx - End interupt/error   |                               |
+--------+---------------------------------+-------------------------------+