170
Western Digital Hard Disk Drive OEM Specification
11.21
Read DMA Ext (25h)
Com m and Block Output Registers
Com m and Block Input Registers
Register
7
6
5
4
3
2
1
0
Register
7
6
5
4
3
2
1
0
Data Low
-
-
-
-
-
-
-
-
Data Low
-
-
-
-
-
-
-
-
Data High
-
-
-
-
-
-
-
-
Data High
-
-
-
-
-
-
-
-
Feature
Current
-
-
-
-
-
-
-
-
Error
...See Below ...
Previous
-
-
-
-
-
-
-
-
Sector Count
Current
V
V
V
V
V
V
V
V
Sector Count
HOB=0
-
-
-
-
-
-
-
-
Previous
V
V
V
V
V
V
V
V
HOB=1
-
-
-
-
-
-
-
-
Sector Number
Current
V
V
V
V
V
V
V
V
Sector Number
HOB=0
V
V
V
V
V
V
V
V
Previous
V
V
V
V
V
V
V
V
HOB=1
V
V
V
V
V
V
V
V
Cylinder Low
Current
V
V
V
V
V
V
V
V
Cylinder Low
HOB=0
V
V
V
V
V
V
V
V
Previous
V
V
V
V
V
V
V
V
HOB=1
V
V
V
V
V
V
V
V
Cylinder High
Current
V
V
V
V
V
V
V
V
Cylinder High
HOB=0
V
V
V
V
V
V
V
V
Previous
V
V
V
V
V
V
V
V
HOB=1
V
V
V
V
V
V
V
V
Device/Head
1
1
1
D
-
-
-
-
Device/Head
-
-
-
-
-
-
-
-
Command
0
0
1
0
0
1
0
1
Status
...See Below ...
Error Register
Status Register
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
CRC
UNC
0
IDN
0
ABT
T0N
AMN
BSY
RDY
DF
DSC
DRQ
COR
IDX
ERR
V
Vs
0
V
0
V
0
0
0
V
0
V
-
0
-
V
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 c ommand 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.
