IDE Interface
                      =============
+------+--------------------+-------------------------------+
|      |      Write         |         Read                  |
+======+====================+===============================+
| FC40 |               Data Low Byte                        |
+------+--------------------+-------------------------------+
| FC41 |  Special Features  |            Error              |
|      |                    | b7: -                         |
|      |                    | b6: UNC  Uncorrectable error  |
|      |                    | b5: MC   Media changed        |
|      |                    | b4: IDNF Sector Not Found     |
|      |                    | b3: MCR  Media Change Request |
|      |                    | b2: ABRT Abort                |
|      |                    | b1: NM   No media present     |
|      |                    | b0: -                         |
+------+--------------------+-------------------------------+
| FC42 |                Sector Count                        |
+------+--------------------+-------------------------------+
| FC43 |         Sector Number or LBA b0-b7                 |
+------+--------------------+-------------------------------+
| FC44 |         Cylinder Low or LBA b8-b15                 |
+------+--------------------+-------------------------------+
| FC45 |        Cylinder High or LBA b16-b23                |
+------+--------------------+-------------------------------+
| FC46 |              LBA+Drive+Head                        |
|      |         b7:    unused                              |
|      |         b6:    0=CHS access, 1=LBA access          |
|      |         b5:    unused                              |
|      |         b4:    Drive                               |
|      |         b3-b0: Head or LBA b24-b27                 |
+------+--------------------+-------------------------------+
| FC47 |       Command      |         Status                |
|      |                    | b7: BSY Busy                  |
|      |                    | b6: DRDY Data Ready           |
|      |                    | b5: DF Device Fault           |
|      |                    | b4: -                         |
|      |                    | b3: DRQ                       |
|      |                    | b2: -                         |
|      |                    | b1: -                         |
|      |                    | b0: ERR Error in reg 1        |
+------+--------------------+-------------------------------+
| FC48 |              Data High Byte                        |
+------+--------------------+-------------------------------+
| FC49-|                Undefined                           |
| FC4D |                                                    |
+------+--------------------+-------------------------------+
| FC4E |   Digital Output   |   Alternative Status          |
|      |                    |   Doesn't reset IRQs          |
+------+--------------------+-------------------------------+
| FC4F |         -          |      Drive Data               |
+------+--------------------+-------------------------------+