Seagate ST3660A Product Manual - Page 36

Set Multiple Mode command C6, Read Multiple command C4

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28 Medalist XE Family Product Manual, Rev. B 3.3.3 Set Multiple Mode command (C6H) Command code C6H enables the drive to perform Read and Write Multiple operations and establishes the block count for these commands. You do not have to issue this command before every Read Multiple or Write Multiple command. The Sector Count register is loaded with the number of sectors per block. Drives normally support block sizes of 2, 4, 8 and 16 sectors. However, other block-size values may also be supported, depending on the size of the drive's buffer. After receiving the Set Multiple Mode command, the drive sets BSY=1 and checks the Sector Count register. If the Sector Count register contains a valid value and the block count is supported, the value is loaded for all subsequent Read Multiple and Write Multiple commands and execution of those commands is enabled. If a block count is not supported, an Aborted Command error is posted, and Read Multiple and Write Multiple commands are disabled. If the Sector Count register contains 0 when the command is issued, Read and Write Multiple commands are disabled. At power on, or after a hardware reset, the default mode is Read and Write Multiple disabled. If Disable Default has been set in the Features register, then the mode remains the same as that last established before a software reset. Otherwise it reverts to the default of disabled. 3.3.4 Read Multiple command (C4H) This command (code C4H) is similar to the Read Sectors command. Interrupts are not generated on every sector, but on the transfer of a block that contains the number of sectors defined by a Set Multiple Mode command. The number of sectors per block to be transferred without intervening interrupts is programmed by the Set Multiple Mode command, which must be executed before the Read Multiple command. Interrupts are generated when DRQ is set to 1 at the beginning of each block or partial block. 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.

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3.3.3
Set Multiple Mode command (C6
H
)
Command code C6
H
enables the drive to perform Read and Write
Multiple operations and establishes the block count for these commands.
You do not have to issue this command before every Read Multiple or
Write Multiple command.
The Sector Count register is loaded with the number of sectors per block.
Drives normally support block sizes of 2, 4, 8 and 16 sectors. However,
other block-size values may also be supported, depending on the size
of the drive’s buffer. After receiving the Set Multiple Mode command, the
drive sets BSY=1 and checks the Sector Count register.
If the Sector Count register contains a valid value and the block count is
supported, the value is loaded for all subsequent Read Multiple and Write
Multiple commands and execution of those commands is enabled. If a
block count is not supported, an Aborted Command error is posted, and
Read Multiple and Write Multiple commands are disabled.
If the Sector Count register contains 0 when the command is issued,
Read and Write Multiple commands are disabled.
At power on, or after a hardware reset, the default mode is Read and
Write Multiple disabled. If Disable Default has been set in the Features
register, then the mode remains the same as that last established before
a software reset. Otherwise it reverts to the default of disabled.
3.3.4
Read Multiple command (C4
H
)
This command (code C4
H
) is similar to the Read Sectors command.
Interrupts are not generated on every sector, but on the transfer of a block
that contains the number of sectors defined by a Set Multiple Mode
command.
The number of sectors per block to be transferred without intervening
interrupts is programmed by the Set Multiple Mode command, which
must be executed before the Read Multiple command. Interrupts are
generated when DRQ is set to 1 at the beginning of each block or partial
block.
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.
28
Medalist XE Family Product Manual, Rev. B