Specifications

5.3.1 Command registers
The following table summarizes the contents of the Command registers
following implementation of the various ATA interface commands. The
following abbreviations are used in this table:
Command type abbreviations:
PIOR PIO read command DMA DMA data transfer commands
PIOW PIO write command ND Nondata commands
Register abbreviations:
FR Features register SC Sector Count register
SN Sector Number register CY Cylinder register
DH Drive/Head register
Parameter abbreviations:
n The register does not contain a valid parameter for this command.
y This register contains a valid parameter used by this command.
In the the Drive/Head register, y means that both drive and head
parameters are valid.
D In the Drive/Head register, only the drive parameter is valid. (*the
Execute Drive Diagnostics command is addressed to drive 0 but
executed by both drives.)
Command name
Type
Command
code
Register
FR SC SN CY DH
ATA standard commands
Execute Drive Diagnostics
ND
90
H
n n n n D*
Format Track
PIOW
50
H
n y n y y
Identify Drive
PIOR
EC
H
n n n n D
Initialize Drive Parameters
ND
91
H
n y n n y
NOP
ND
00
H
n n n n y
Read Buffer
PIOR
E4
H
n n n n D
continued
ATA Interface Reference Manual, Rev. C 33