4. IDE Interface
22
Sector Number Register
(1F3h, Read/Write - 8 bits)
This register contains the starting sector number for any disk access. The sector
number is a value between 1 and the maximum number of sectors per track. At the
completion of each sector, and at the end of the command, this register is updated to
reflect the last sector read correctly, or the sector on which the error occurred. During
multiple sector transfers this register is updated to point to the next sector to be
read/written if the previous sector's operation was successful.
Cylinder Low Register
(1F4h, Read/Write - 8 bits)
The cylinder low register contains the low order 8 bits of the starting cylinder address for
any disk access. On multiple sector transfers that cross cylinder boundaries, the host
updates this register when the command is executed, to reflect the current cylinder
number. The high order 8 bits are handled by the cylinder high register described next.
Cylinder High Register
(1F5h, Read/Write - 8 bits)
The cylinder high register contains the high order 8 bits of the starting cylinder address
for any disk access. On multiple sector transfers that cross cylinder boundaries, the host
updates this register when the command is executed, to reflect the current cylinder
number. The low order 8 bits are handled by the Cylinder Low Register described
above.
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