ATA Command Description
SanDisk CompactFlash Card OEM Product Manual
5.1.11
Read Multiple–C4H
The Read Multiple command performs similarly to the Read Sectors command. Interrupts are
not generated on every sector, but on the transfer of a block, which contains the number of
sectors defined by a Set Multiple, command.
Table 5-18
Read Multiple
Bit
7
6
5
4
3
2
1
0
Command (7)
C4H
C/D/H (6)
1
LBA
1
Drive
Head (LBA 27-24)
Cyl High (5)
Cylinder High (LBA 23-16)
Cyl Low (4)
Cylinder Low (LBA 15-8)
Sec Num (3)
Sector Number (LBA 7-0)
Sec Cnt (2)
Sector Count
Feature (1)
X
Command execution is identical to the Read Sectors operation except that the number of
sectors defined by a Set Multiple command is transferred without intervening interrupts. DRQ
qualification of the transfer is required only at the start of the data block, not on each sector.
The block count of sectors to be transferred without intervening interrupts is programmed by
the Set Multiple Mode command, which must be executed prior to the Read Multiple
command. When the Read Multiple command is issued, the Sector Count Register contains the
number of sectors (not the number of blocks or the block count) requested. If the number of
requested sectors is not evenly divisible by the block count, as many full blocks as possible are
transferred, followed by a final, partial block transfer. The partial block transfer is for n
sectors, where:
n = (sector count)-module (block count)
.
If the Read Multiple command is attempted before the Set Multiple Mode command has been
executed or when Read Multiple commands are disabled, the Read Multiple operation is
rejected with an Aborted Command error. Disk errors encountered during Read Multiple
commands are posted at the beginning of the block or partial block transfer, but DRQ is still
set and the data transfer will take place as it normally would, including transfer of corrupted
data, if any.
Interrupts are generated when DRQ is set at the beginning of each block or partial block. The
error reporting is the same as that on a Read Sector(s) Command. This command reads from 1
to 256 sectors as specified in the Sector Count register. A sector count of 0 requests 256
sectors. The transfer begins at the sector specified in the Sector Number Register.
At command completion, the Command Block registers contain the cylinder, head and sector
number of the last sector read.
If an error occurs, the read terminates at the sector where the error occurred. The Command
Block registers contain the cylinder, head and sector number of the sector where the error
occurred. The flawed data is pending in the sector buffer.
Subsequent blocks or partial blocks are transferred only if the error was a correctable data
error. All other errors cause the command to stop after transfer of the block that contained the
error.
02/07, Rev. 12.0
5-16
© 2007 SanDisk Corporation
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