Seagate Medalist 1640 Product Manual page 40

32 Medalist 1640 and 2140 Product Manual, January 1996
To use the command:
1. Write the feature value to the Features register.
2. Write the Set Features command to the command register.
Note. If the value in the Features register is not supported or is invalid,
the drive posts an Aborted Command error (04).
The factory-default values are restored at power-on or after a hard reset.
3.2.2.1 Write cache (02
Write cache facilitates the transfer of data from the host to the drive. It
allows the host to send contiguous write commands to the drive while
the data is being written to the media. As soon as all the current write
command data has been transferred into the drive's buffer, it will issue a
command complete status.
Caution. Although the drive issues a write complete when it has re-
ceived all of the data from the host, it continues to write data
to the media until the buffer is empty. If the host issues a hard
reset or if the power is cycled down before the buffer is cleared,
the data remaining in the buffer or not written to the media is
lost.
3.2.2.2 PIO and DMA data-transfer modes
You can set the multiword DMA mode and identify the PIO data-transfer
mechanism and transfer mode with the Set Features command. To set
the multiword DMA mode:
1. 1. Write Set Features command value 03
the Features register.
2. Write a transfer types value to the Sector Count register. The upper 5
bits of this value define the type of data transfer, and the lower 3 bits
encode the mode value.
This changes word 63 of the Identify Drive command to the mode you
enter in the Sector Count register.
The table on the next page identifies allowable transfer types values:
)
H
(Set Data Transfer mode) to
H