Specifications

5.4.15 Set Multiple Mode command

This command (command code C6

) enables the drive to perform Read

and Write Multiple operations and establishes the block count for these

commands.

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. Upon receipt of 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.

This command is not required prior to every Read Multiple or Write

Multiple command.

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

to a software reset, otherwise it reverts to the default of disabled.

5.4.16 Write Buffer command

This command (command code E8

) allows the host to overwrite the

contents of the drive’s sector buffer with any data pattern desired.

The Read Buffer and Write Buffer commands are synchronized within

the drive such that sequential Write Buffer and Read Buffer commands

access the same 512 bytes within the buffer.

5.4.17 Write DMA command

This command (command codes CA

and CB

) executes in a similar

manner to Write Sectors except for the following:

• The host initializes a slave-DMA channel prior to issuing the com-

mand.

• Data transfers are qualified by DMARQ and are performed by the

slave-DMA channel.

52 ATA Interface Reference Manual, Rev. C