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11.20 Read DMA(C8h/C9h)
Com m and Block Output Registers
Register
7
6
Data
-
-
Feature
-
-
Sector Count
V
V
Sector Number
V
V
Cylinder Low
V
V
Cylinder High
V
V
Device/Head
1
L
Command
1
1
Error Register
7
6
5
4
CRC UNC
0
IDN
V
V
0
V
Table 139 Read DMA Command (C8h/C9h)
The Read DMA command reads one or more sectors of data from disk media, 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.
5
4
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
D
H
H
H
H
0
0
1
0
0
R
3
2
1
0
0
ABT
T0N AMN
0
V
0
0
Western Digital Hard Disk Drive OEM Specification
Com m and Block Input Registers
Register
7
6
Data
-
-
Error
Sector Count
V
V
Sector Number
V
V
Cylinder Low
V
V
Cylinder High
V
V
Device/Head
-
-
Status
Status Register
7
6
5
4
BSY RDY
DF
DSC DRQ COR
0
V
0
V
168
5
4
3
2
1
0
-
-
-
-
-
-
...See Below ...
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
-
-
H
H
H
H
...See Below ...
3
2
1
0
IDX
ERR
-
0
-
V
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