DESKTOP x1k12
                                ͻ
                                   DMA-FDC/HDC   
                                 bit assignments 
                                ͼ
                                 Atari Direct Memory Access for
                                 Floppy Disk Controller and Hard Disk Controller
              Ŀ
               Status Register      b2=data requested
                                       0:no
                                       1:yes
                                    b1=sector counter equals zero
                                       0:yes
                                       1:no
                                    b0=error
                                       0:yes
                                       1:no
              
             Ŀ
              Control Register      b8=Read/Write
                                       0:read
                                       1:write
                                    b4=FDC-HDC/SC
                                       0:FDC-HDC
                                       1:sector counter
                                    b3=FDC/HDC
                                       0:FDC
                                       1:HDC
                                 b2-b1=[b1-b0]=FDC/HDC register
                                               00:FDC-SR/CR
                                               01:FDC-TKR
                                               10:FDC-SCR
                                               11:FDC-DTR
             
 Ŀ
  Direct Memory Access Counter [b23-b0]=direct memory access counter
                                        (low-middle-high for writing)
 
               Ŀ
                Sector Counter   b7-b0=sector counter
                                       (1 sector=512 bytes)
               






                           Ŀ
                                      DMA           
                              Ŀ   
                Ŀ     16 bytes buffer      Ŀ Ŀ
                 Memory Ĵ FDC/HDC Ĵ Disk 
                     16 bytes buffer       
                                 
                           
