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10.8.23 Read DMA (C8h/C9h)
COMMAND CODE
1 1 0 0 1 0 0 X
REGISTER
REGISTER SETTING
NORMAL COMPLETION
DR
drive no.
no change
CY
starting cylinder
last possible
HD
starting head
last possible
SN
starting sector
last possible
SC
no. of sector to read
00H
FT
no
change
LBA
staring address
last address
This command is basically identical to Sector command except following features.
•
Host initialize the DMA channel before issuing command.
- Data transfer is initiated by DMARQ and handled by the DMA channel in the host.
- Drive issues only one interrupt at the completion of each command to show the status is valid after data
transfer.
During DMA transfer phase, either BSY or DRQ is set to 1.
When a command is completed, CY, HD, SN register (LBA register) shows the sector transferred the latest.
If the drive detects unrecoverable error, the drive terminate the command and CY, HD, SN register (LBA
register) shows the sector where error occurred.
10.8.24 Read DMA EXT (25h)
COMMAND CODE
0 0 1 0 0 1 0 1
REGISTER
REGISTER SETTING
NORMAL COMPLETION
DR
drive no.
no change
LBA
Low
Current
Previous
LBA(7:0)
LBA(31:24)
HOB=0
HOB=1
last address
last address
LBA
Mid
Current
Previous
LBA(15:8)
LBA(39:32)
HOB=0
HOB=1
last address
last address
LBA
High
Current
Previous
LBA(23:16)
LBA(47:40)
HOB=0
HOB=1
last address
last address
SC Current
Previous
sector count(7:0)
sector count(15:8)
HOB=0
HOB=1
00H
00H
FT Current
Previous
reserved
reserved
HOB=0
HOB=1
no change
no change
This command is basically identical to Read DMA command except register setting.
This command is available in LBA addressing only.