solidsk 1770 issue 1 registers:

FE80	Status/Command register
FE81	Track register
FE82	Sector register
FE83	Data register
FE87    Control register
	bit 0	0=drive 0, 1=drive 1
	bit 1	0=side 0, 1=side 1
	bit 2	0=double density, 1=single density
	bit 3	
	bit 4	
	bit 5	
	bit 6	
	bit 7	

Drive control register
======================

  This controls various functions that the 177X is unable to:

  Master drive control:
        Bit       Meaning
        -----------------
        7,6       Not used.
         5        Double density select (0 = double, 1 = single).
         4        Side select (0 = side 0, 1 = side 1).
         3        Drive select 2.
         2        Reset drive controller chip.
         1        Drive select 1.
         0        Drive select 0.

  B+ drive control:
        Bit       Meaning
        -----------------
        7,6       Not used.
         5        Reset drive controller chip.
         4        Interrupt ?
         3        Double density select (0 = double, 1 = single).
         2        Side select (0 = side 0, 1 = side 1).
         1        Drive select 1.
         0        Drive select 0.

  Opus double density board on BBC:
        Bit       Meaning
        -----------------
        7         Not used.
        6         Density select (0 = single, 1 = double).
        5-2       Not used.
        1         Side select (0 = side 0, 1 = side 1).
        0         Drive select (0 = drive 0, 1 = drive 1).

  Note that only 1 drive select bit line should be set at a time.

Addresses of registers:
=======================

   Computer        Location of disk chip & chip  Location of drive control
   ---------------------------------------------------------------------
   BBC B with Opus     &FE80 - &FE83    WD1770             &FE84
   BBC B+              &FE84 - &FE87    WD1770             &FE80
   BBC Master          &FE28 - &FE2B    WD1770             &FE24
   Archimedes                ?          WD1772               ?

  I am aware that some archimedes used the WD1772 is used, but if anyone
  knows the addresses, I will be happy to put them in.