Alternate Status Register; Command Register; Cylinder High Register; Cylinder Low Register - IBM IC25N020ATDA04 - Travelstar 20 GB Hard Drive Specifications

10.1 Alternate Status Register

Alternate Status Register
7 6 5 4 3 2 1 0
BSY RDY DF DSC DRQ COR IDX ERR

Figure 54. Alternate Status Register

This register contains the same information as the Status Register. The only difference between this
register and the Status Register is that reading the Alternate Status Register does not imply an interrupt
acknowledge or a clear of a pending interrupt. See Section 10.12, "Status Register" on page 76 for the
definition of the bits in this register.

10.2 Command Register

This register contains the command code being sent to the device. Command execution begins
immediately after this register is written. The command set is shown in Figure 73 on page 109. All other
registers required for the command must be set up before writing to the Command Register.

10.3 Cylinder High Register

This register contains the high order bits of the starting cylinder address for any disk access. At the end of
the command this register is updated to reflect the current cylinder number.
In LBA Mode this register contains Bits 16–23. At the end of the command this register is updated to
reflect the current LBA Bits 16–23.
The cylinder number may be from zero to the number of cylinders minus one.

10.4 Cylinder Low Register

This register contains the low order 8 bits of the starting cylinder address for any disk access. At the end
of the command, this register is updated to reflect the current cylinder number.
In LBA Mode this register contains Bits 8–15. At the end of the command, this register is updated to reflect
the current LBA Bits 8–15.
The cylinder number may be from zero to the number of cylinders minus one (1).
Travelstar 48GH, 30GN & 15GN hard disk drive specifications
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