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11.21 Read DMA Ext (25h)
Com m and Block Output Registers
Register
Data Low
Data High
Current
Feature
Previous
Current
Sector Count
Previous
Current
Sector Number
Previous
Current
Cylinder Low
Previous
Current
Cylinder High
Previous
Device/Head
Command
Error Register
7
6
5
CRC
UNC
0
IDN
V
Vs
0
Table 140 Read DMA Ext Command (25h)
The Read DMA command reads one or more sectors of data from disk media, and then transfers the data from the
device to the host.
The sectors are transferred through the Data Register 16 bits at a time.
The host initializes a slave-DMA channel prior to issuing the command. The data transfers are qualified by DMARQ
and are performed by the slave-DMA channel. The device issues only one interrupt per command to indicate that
data transfer has terminated and status is available.
If an uncorrectable error occurs, the read will be terminated at the failing sector.
7
6
5
4
3
2
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
1
1
1
D
-
-
0
0
1
0
0
1
4
3
2
1
0
ABT
T0N
V
0
V
0
Western Digital Hard Disk Drive OEM Specification
Com m and Block Input Registers
1
0
Register
-
-
Data Low
-
-
Data High
-
-
Error
-
-
V
V
Sector Count
V
V
V
V
Sector Number
V
V
V
V
Cylinder Low
V
V
V
V
Cylinder High
V
V
-
-
Device/Head
0
1
Status
0
7
6
AMN
BSY
RDY
0
0
V
170
7
6
5
4
-
-
-
-
-
-
-
-
...See Below ...
HOB=0
-
-
-
-
HOB=1
-
-
-
-
HOB=0
V
V
V
V
HOB=1
V
V
V
V
HOB=0
V
V
V
V
HOB=1
V
V
V
V
HOB=0
V
V
V
V
HOB=1
V
V
V
V
-
-
-
-
...See Below ...
Status Register
5
4
3
2
DF
DSC
DRQ
COR
0
V
-
0
3
2
1
0
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
-
-
-
-
1
0
IDX
ERR
-
V
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