SCSI Interface
                      ==============

+------+--------------------+------------------------+
|      |      Write         |         Read           |
+======+====================+========================+
| FC40 |                  Data                       |
+------+--------------------+------------------------+
| FC41 |       -            |        Status          |
|      |                    | b7: 0=Command, 1=Data  |
|      |                    | b6: 0=Input, 1=Output  |
|      |                    | b5: REQ                |
|      |                    | b4: INTs enabled       |
|      |                    | b3: 0                  |
|      |                    | b2: 0                  |           
|      |                    | b1: BUSY               |
|      |                    | b0: MSG                |
+------+--------------------+------------------------+
| FC42 |   Write Select     |           -            |
|      |  Data irrelevant   |                        |
+------+--------------------+------------------------+
| FC43 | Interupt Enable    |           -            |
|      | b7: 0=disable INTs |                        |
|      |     1=enable INTs  |                        |
+------+--------------------+------------------------+