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12.18 Read DMA(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
Table 118 Read DMA Command (C8h/C9h)
Command Input
Field
Description
FEATURE
N/A
COUNT
The number of logical sectors to be transferred. A value of 00h indicates
that 256 logical sectors are to be transferred
LBA
LBA of first logical sector to be transferred
DEVICE
Bit Description
7 Obsolete
6 N/A
5 Obsolete
4 Transport Dependent
3:0 Reserved
Command
7:0 C8h or C9h
Normal Outputs
See Normal Outputs in 12.7 Flush Cache (E7h)
Error Outputs
Field
Description
ERROR
Bit Description
7 INTERFACE CRC bit
6 UNCORRECTABLE ERROR bit
5 Obsolete
4 ID NOT FOUND bit
3 Obsolete
2 ABORT bit
1:0 Obsolete
COUNT
N/A
LBA
LBA of First Unrecoverable Error
DEVICE
Bit Description
7 Obsolete
6 N/A
5 Obsolete
4 Transport Dependent
3:0 Reserved
STATUS
Bit Description
7:6 Transport Dependent
5 DEVICE FAULT bit
4 N/A
3 Transport Dependent
2 N/A
1 SENSE DATA AVAILABLE bit
0 ERROR bit
186
Hard Disk Drive Specification