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

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COMMON COMMAND SET AND DISK OPERATION

NOTES:	1.	Number of cylinders is taken from the attach packet byte
		offset $08.
	2.	Number of heads is taken from the attach packet byte offset
		$07.
	3.	Starting cylinder - write precomp is taken from the attach
		packet byte offset $0A.
	4.	Starting cylinder - reduced write current is left as the
		default value as returned from the mode sense command.
	5.	The drive step rate is specified in the attach packet, byte
		offset $05 in units of 40 microseconds. This value is
		converted to 100 nanoseconds units before writing to page
		4 of the mode select command. A value of zero in the
		attach packet causes the drive to use the default value.
	6.	Landing zone cylinder is left as the default value as
		returned from the mode sense command.
	7.	This field is left as the default value as returned from the
		mode sense command.

Before accessing a floppy disk on the OMTI7000, the MVME147 SCSI firmware sends a mode select command 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		2C	Parameter list length
5		00	Control byte: no link, no flag

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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