SCSI Command Set Summary
                      ========================
    
    +-----+--------------------------------------------+
    | &00 | Test drive ready                           |
    | &01 | Restore to track zero                      |
    | &02 | reserved                                   |
    | &03 | Request sense status (SCSI result)         |
    | &04 | Format drive                               |
    | &05 | Check track format                         |
    | &06 | Format track                               |
    | &07 | Format bad track                           |
    | &08 | Read                                       |
    | &09 | Read Verify                                |
    | &0A | Write                                      |
    | &0B | Seek                                       |
    | &0C | Initialise drive characteristics           |
    | &0D | Read ECC burst error length                |
    | &0E | Format Alternative Track                   |
    | &0F | Write Sector Buffer                        |
    +-----+--------------------------------------------+
    | &10 | Read Sector Buffer                         |
    | &12 | Read device identity string                |
    | &15 | Write drive characteristics                |
    | &1A | Read drive characteristics                 |
    | &1B | Park heads/Start/stop unit                 |
    |     |                                            |
    +-----+--------------------------------------------+
    |     |                                            |
    | &2F | Verify drive                               |
    +-----+--------------------------------------------+
    | &70 | RAM diagnostic                             |
    | &71 | reserved                                   |
    | &72 | reserved                                   |
    | &73 | Drive diagnostic                           |
    | &74 | Controller internal diagnostics            |
    | &75 | Read long                                  |
    | &76 | Write long                                 |
    |     |                                            |
    +-----+--------------------------------------------+
    |     |                                            |
    | &C8 | Read F-code result from LVdos (LVFS)       |
    | &CA | Transmit F-code to LVdos (VLFS)            |
    |     |                                            |
    +-----+--------------------------------------------+
    | &E0 | RAM Diagnostic                             |
    | &E1 | Reserved                                   |
    | &E2 | Reserved                                   |
    | &E3 | Drive Diagnostic                           |
    | &E4 | Controller Internal Diagnostics            |
    | &E5 | Read Long                                  |
    | &E6 | Write Long                                 |
    | &E7 | Retry Statistics                           |
    |     |                                            |
    +-----+--------------------------------------------+

                           SCSI Status and Errors
                           ----------------------

Some Acorn documents list SCSI errors in the range &20-&2F, and some
documents list them in the range &60-&6F. The hardware controller documents
list then in the &20-&2F range. What is not made clear is that bit 6 is used
to indicate if the error is from the hard drive controller or the floppy
controller. Floppy errors are the same as hard drive errors, ORed with &40.
Floppy errors are also the 1770 status byte ORed with &40.

  Error
  &00  Ok
  &01  No index - is drive formatted?
  &02  Drive door open/Seek error/Seek not completed
  &03  Write fault/Media error (disc dirty)
  &04  Drive not ready
  &05  Malformed SCSI command
  &06  Track 0 not found

  &10  ID CRC error - ECC error in ID field - sector not found
  &11  Data CRC error - ECC error in data field
  &12  Address mark not found (sector found but no data)
  &13  unused
  &14  Seek error - Sector not found
  &15  Seek error - Track not found
  &16  unused
  &17  unused
  &18  Correctable data error/Data CRC error
  &19  Bad Track flag set in track accessed
  &1A  Format error - track not formatted/wrong interleave/ID ECC error
  &1B  unused
  &1C  Unformatted or bad format
  &1D  unused
  &1E  unused
  &1F  unused
                                        Floppy Errors
  &20  Invalid command to controller    &60  Bad command      
  &21  Illegal disc address             &61  Bad disc address 
  &22  unused
  &23                                   &63  Volume error     
  &24  Invalid parameter to controller  &64  Bad argument
  &25  Illegal drive number             &65  Bad drive        
  &26  unused
  &27                                   &67  Unsupported SCSI command
  &28  Cartridge changed
  &29
  &2A
  &2B
  &2C  Error count overflow
  &2D
  &2E
  &2F                                   &6F  Abort (Escape)

  &30  Controller RAM error
  &31  Controller program memory CRC error
  &33  ECC polynominal error

  &40  Write protected  (floppy)
  &48  CRC error        (floppy)
  &50  Sector not found (floppy)

  &7F  Unknown SCSI result