Alternate Status Register; Command Register; Cylinder High Register; Cylinder Low Register - IBM IC35L040AVVN07-0 - 40GB IDE Deskstar 120GXP 7200RPM UATA-100 07N9682 Specifications

8.1 Alternate Status Register

Figure 69. Alternate Status Register

This register contains the same information as the Status Register. The only difference is that reading this
register does not imply interrupt acknowledge or clear a pending interrupt. See 8.13, "Status Register" on
page 72 for the definition of the bits in this register.

8.2 Command Register

This register contains the command code being sent to the device. Command execution begins immedi-
ately after this register is written. The command set is shown in Figure 88 on page 104.
All other registers required for the command must be set up before writing the Command Register.

8.3 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 range from zero to the number of cylinders minus one.

8.4 Cylinder Low Register

This register contains the low 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 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.
Alternate Status Register
7 6 5
DSC/
BSY RDY DF
SERV
Deskstar 120GXP hard disk drive specifications
4 3 2 1
DBQ COR IDX
68
0
ERR