DESKTOP x1k10                                ͻ
                                      WD1772     
                                 bit assignments 
                                ͼ
                                 Western Digital 1772
              Ŀ
               Status Register   b0=busy
                                 b1=index pulse/data requested (type I/II-III)
                                 b2=track 0    /lost data      (type I/II-III)
                                 b3=cyclic redundancy checksum error
                                 b4=record not found
                                 b5=spin up/DAM type ($FB/$F8 for read sector)
                                 b6=write protected
                                 b7=motor on (~10 index pulses after command)
              
             Ŀͻ
              Command Register       bit          command      type
                               7 6 5 4 3 2 1 0                     
                               ͹
                               0000hv11 restore           I 
                               Ķ
                               0001hv11 seek              I 
                               Ķ
                               001uhv11 step              I 
                               Ķ
                               010uhv11 step in           I 
                               Ķ
                               011uhv11 step out          I 
                               Ķ
                               100mh000 read  sector     II 
                               Ķ
                               101mh00d write sector     II 
                               Ķ
                               1100h000 read address    III 
                               Ķ
                               1110h000 read  track     III 
                               Ķ
                               1111h000 write track     III 
                               Ķ
                               1101int00 force interrupt  IV 
                               ͼ
                                        h: motor on test
                                          v: verify track
                                      u: update track register
                                      m: multiple sectors
                                              d: DAM type ($FB/$F8)
                                        int: 00:without interrupt
                                             10:with    interrupt
                                             01:after index pulse
                               set   interrupt requested when command is over
                               clear interrupt requested when   SR    is read
                               Ŀ
                                              write track                   
                               Ĵ
                                byte in  byte out MFM     type           
                               Ĵ
                                $00-$F4   $00-$F4 yes data or gap        
                               Ĵ
                                  $F5       $A1    no sync/clearCRC      
                               Ĵ
                                  $F6       $C2    no synchronization    
                               Ĵ
                                  $F7     $ss-$ss  no write CRC          
                               Ĵ
                                  $F8       $F8    no data address mark  
                               Ĵ
                                  $F9       $F9    no data mark          
                               Ĵ
                                  $FA       $FA    no data mark          
                               Ĵ
                                  $FB       $FB    no data address mark  
                               Ĵ
                                  $FC       $FC    no data mark          
                               Ĵ
                                  $FD       $FD    no data mark          
                               Ĵ
                                  $FE       $FE    no index address mark 
                               Ĵ
                                  $FF       $FF    no data mark          
             
                 Ŀ
                 TracK Register  b7-b0=track
                 
                Ŀ
                SeCtor Register  b7-b0=sector
                
                  Ŀ
                  DaTa Register  b7-b0=data/track to seek
                  
