0320-0323 ---- XT HDC 1   (Hard Disk Controller)


0320   r/w data register

0321   w   reset controller
   r   read controller hardware status
        bit 7-6 = 0
        bit 5        logical unit number
        bit 4-2 = 0
        bit 1   = 0  no error
        bit 0   = 0

0322   r   read DIPswitch setting on XT controller card
   w   generate controller-select pulse
0323   w   write pattern to DMA and INT mask register

0324-0327 ---- XT HDC 2   (Hard Disk Controller)
0328-032B ---- XT HDC 3   (Hard Disk Controller)
032C-032F ---- XT HDC 4   (Hard Disk Controller)