3.1.5MODE SELECT (15)
Byte | Bit | 7 | 6 | 5 | 4 |
| 3 | 2 | 1 | 0 |
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0 |
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| X‘15’ |
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1 |
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| LUN |
| PF |
| 0 | 0 | 0 | SP |
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2 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
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3 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
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4 |
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| Parameter List Length |
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5 |
| 0 | 0 | 0 | 0 | 0 | 0 | Flag | Link | |
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This command performs setting and changing of each type of parameter related to disk drive physical attributes, data format, timing of SCSI bus disconnect/reconnect processing and error recovery procedures, etc. The INIT can know the types of parameters, the current settings of each parameter and the types of parameters which can be changed, and the ranges for such changes, etc. by using the MODE SENSE or MODE SENSE EXTENDED command.
The data (MODE SELECT parameters) transferred from the INIT to the IDD by this command, are configured from a "Header," "Block Descriptor" and one or more "Page Descriptors" which describe each parameter, each of which will be explained later.
When the "PF (page format)" bit in CDB byte 1 is "1," it indicates that the MODE SELECT parameters transferred from the INIT by this command are in the "Page Descriptor" format. The IDD disregards the value specified in this bit and regards the MODE SELECT parameters transferred from the INIT as being in the "Page Descriptor" format and executes this command.
The "SP (save pages)" bit in CDB byte 1 specifies whether or not to save the MODE SELECT parameters specified in this command on the disk. It is possible for the IDD to save all the MODE SELECT parameters described in the "Page Descriptor" (except for those on page C), but this bit's specification is valid only for parameters other than "Format parameters (Page 3)" and "Drive parameters (Page 4: excluding byte 17)."
If "1" is specified in the "SP" bit, the parameters transferred from the INIT are saved to the disk when this command is executed, except for "Format parameters (page 3)" and "Drive parameters (Page 4: excluding byte 17)." When the "SP" bit is "0," these parameters are not saved to the disk. On the other hand, as for "Format parameters (Page 3)" and "Drive parameters (Page 4: excluding byte 17)," regardless of the specification of the "SP" bit when this command is executed, these parameters are always saved to the disk when the FORMAT UNIT command is executed.
The "Parameter length" field of the CDB specifies the total byte length of the MODE SELECT parameters transferred from the INIT by this command. If zero is specified in the "Parameter length" field, this command is terminated normally without data transfer being executed with the INIT. The MODE SELECT parameters have specifically defined formats and lengths, as explained by the descriptions of each page descriptor in this item, and the INIT must always specify (transfer) those formats and lengths.
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