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ATAPI Interface Chapter 5
STT8000A Product Manual Page 47
Mode Select command
Bit
Byte
76543210
0 Operation code (15h)
1 Reserved 1 (PF) Reserved
2 Reserved
3 (MSB) Parameter List Length
4 (LSB)
5 Reserved
The Mode Select command provides a means to change device parameters. The
PF (Page Format) bit is 1, since the Mode Pages are in SCSI-2 format. The only
changeable parameters are Speed Selection (in the Mode Parameter Header), and
certain fields in Mode Page 2Bh (MFM mode). The Parameter List Length field
specifies the length in bytes of the Mode Select parameter list that are transferred to
the device as data. A Parameter List Length of zero indicates that no data is
transferred.
Mode Sense should be issued prior to Mode Select to determine the supported
pages, page lengths, and other parameters.
The device terminates the Mode Select command with a Check Condition status,
sets the Sense Key to Illegal Request, and sets the Additional Sense Code to
Invalid Field in Parameter List for the following conditions:
• If an attempt is made to change an unchangeable value in the Mode Select
header, block descriptor, or any page.
• If an attempt is made to send a page with a length not equal to the parameter
length reported for that page by the Mode Sense command.
• If an attempt is made to send a value for a parameter that is outside the range
supported by the device.