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10.18.1.3 SCT Command Nesting and intermingling with Standard commands
In general, standard ATA commands can be intermingled with SCT Commands but SCT commands cannot be nested.
SCT commands that do require a follow-on data transfer operation never have an issue with being intermixed with
any ATA commands or each other. SCT commands that do require data transfer, on the other hand, may not be
nested; that is, if a key command that requires a data transfer is issued, all data transfer – to or from the host – must
complete before another SCT command is issued. In most cases, however, ATA read/write commands may be
inserted in between SCT data transfers, that is, between complete SMART Read Log/Write Log commands.
Furthermore, any reset (power-on, software or hardware) will cause the SCT command to be aborted.
10.18.1.4 Resets
If an SCT command is executing, any reset including Soft Reset, Hard Reset, COMRESET, and Power-On Reset all
cause the command to be terminated. This could result in partial command execution or data loss. There is no
indication once the drive becomes ready that the previous command was terminated.
10.18.2
SCT Command Protocol
10.18.2.1 Command Transport
SCT Command Transport occurs when a 512-byte data packet (called “Key Sector”) is created and the written to
SMART or extended log page E0h. The key sector specifies Action and Function Codes along with the parameters
that are required to perform the action.
10.18.2.1.1
Issue SCT Command Using SMART
Table 40 Output Registers of SCT Command Using SMART
Command Block Output Registers
Register
7 6 5 4 3 2 1 0
Feature
D6h
Sector Count
01h
Sector Number
E0h
Cylinder Low
4Fh
Cylinder High
C2h
Device/Head
-
-
-
D -
-
-
-
Command
B0h
Table 41 Input Registers of SCT Command Using SMART
Command Block Input Registers (Success)
Command Block Input Registers (Error)
Register
7 6 5 4 3 2 1 0 Register
7 6 5 4 3 2 1 0
Error
00h
Error
04h
Sector Count
Depends on command
(LSB)
Sector Count
Extended Status code
(LSB)
Sector Number
Depends on command
(MSB)
Sector Number
Extended Status code
(MSB)
Cylinder Low
Number of sectors to
transfer (LSB)
Cylinder Low
Number of sectors to
transfer (LSB)
Cylinder High
Number of sectors to
transfer (MSB)
Cylinder High
Number of sectors to
transfer (MSB)
Device/Head
-
-
-
-
-
-
-
-
Device/Head
-
-
-
-
-
-
-
-
Status
50h
Status
51h
86
Hard Disk Drive Specification