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2.0 Registers
In Serial ATA, the host adapter contains a set of registers that shadow the contents of the traditional device regis-
ters, referred to as the Shadow Register Block. Shadow Register Block registers are interface registers used for
delivering commands to the device or posting status from the device. About details, please refer to the Serial ATA
Specification.
In the following cases, the host adapter sets the BSY bit in its shadow Status Register and transmits a FIS to the
device containing the new contents.
•
Command register is written in the Shadow Register Block
•
Device Control register is written in the Shadow Register Block with a change of state of the SRST bit
•
COMRESET is requested
2.1 Alternate Status Register
Table 1: Alternate Status Register
7
BSY
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 "Status Register" on page 7 for the defini-
tion of the bits in this register.
2.2 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 Table 14: 'Command Set (1 of 2)" on page 43 and Table
15: 'Command Set (2 of 2)" on page 44. All other registers required for the command must be set up before writ-
ing to the Command Register.
2.3 Cylinder High Register
This register contains the high order bits of the starting cylinder address for any disk access. At the end of the com-
mand, 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.
When 48-bit addressing commands are used, the "most recently written" content contains LBA Bits 16-23 and the
"previous content" contains Bits 40-47.
Alternate Status Register
6
5
4
DSC/
RDY
DF
SERV
Deskstar 7K500 Hard Disk Drive Serial ATA Addendum
3
2
DRQ
COR
3
1
0
IDX
ERR
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