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11.8.5 Read Sector (20h/21h)
COMMAND CODE
0 0 1 0 0 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
Setting BSY bit, the drive will seek to the target cylinder if the head is not on target track ( implied seek ), select
the head and begin to read the number of sector defined in SC register ( 1-256 ) starting from the target sector.
After finding ID of target sector and having 1 sector of data read into the buffer RAM, the drive sets DRQ in
status register and generates interrupt to report to the host that the drive is ready to transfer the next data.
In case of multi-sector transfer, DRQ bit is reset and BSY is set after 1 sector transfer to prepare for the next
sector transfer.
An uncorrectable data can also be transferred but the subsequent operation will terminate at the cylinder, head,
and sector (or LBA) position in the TASK FILE register. When a sector is ready to be read by the host, an
interrupt is issued. After the last sector is read by the host, no interrupt is issued at the end of a command.
11.8.6 Read Sector EXT (24h)
COMMAND CODE
0 0 1 0 0 1 0 0
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
Setting BSY bit, the drive will seek to the target cylinder if the head is not on target track ( implied seek ), select
the head and begin to read the number of sector defined in SC register ( 1-65536 ) starting from the target
sector. After finding ID of target sector and having 1 sector of data read into the buffer RAM, the drive sets DRQ
in status register and generates interrupt to report to the host that the drive is ready to transfer the next data.
In case of multi-sector transfer, DRQ bit is reset and BSY is set after 1 sector transfer to prepare for the next
sector transfer.
An uncorrectable data can also be transferred but the subsequent operation will terminate at the LBA position
in the TASK FILE register. When a sector is ready to be read by the host, an interrupt is issued. After the last
sector is read by the host, no interrupt is issued at the end of a command.
This command is available in LBA addressing only.