Emerson MVME147 manual Common Command Set And Disk Operation, Notes, Byte Offset

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COMMON COMMAND SET AND DISK OPERATION

NOTES:	1.	If the retry field in the attach packet byte offset $1B is = 00, the
		DCR (disable correction) bit is set and the read retry count field is
		set to 00.
		If the retry field in the attach packet byte offset $1B is NOT = 00,
		the fields at byte 2 and 3 are left as the default value as returned
		from the mode sense command.
	2.	This field is left as the default value as returned from the mode
		sense command.

Before formatting a Winchester disk, the MVME147 SCSI firmware sends a mode select command for format parameters (page 3) to the controller. Below is the command descriptor block for the mode select command:

Mode Select Command CDB

	BYTE OFFSET	VALUE	COMMENTS
0	15	Command code
1		10	LUN = 0, PF = 1, SP = 0
2		00	Reserved
3		00	Reserved
4		(Note)	Parameter list length
5		00	Control byte: no link, no flag

NOTE:	If all of the parameters match or are not changeable,
	only the mode select header and block descriptor is
	sent, and the parameter list length is be $0C.
	If a parameter is changed based on the current,
	changeable, and the packet parameter, the entire page
	3 including the mode select header and the block
	descriptor is sent, and the parameter list length is $24.

The first twelve bytes that are transferred during the DATA OUT phase for the mode select command make up the mode select header, and the block descriptor which is described below:

Mode Select Header and Block Descriptor

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