Emerson MVME147 manual Byte Offset

A

COMMON COMMAND SET AND DISK OPERATION

	BYTE	VALUE	COMMENTS
1	01	Extended message
2		03	Extended message length
3		01	Synchronous data transfer
			request
4		32	Transfer period (50 times 4 ns
			= 200 ns
5		05	REQ/ACK offset
	Test Unit Ready Command CDB

	BYTE OFFSET	VALUE	COMMENTS
0	00	Command code
1		00	LUN is inserted into bits 7-5
2		00	Reserved
3		00	Reserved
4		00	Reserved
5		00	Control byte: no link, no flag

The firmware sends a mode sense command for page 3, current values. The returned block size is compared to the block size in the packet; if they are not the same, the firmware sets a internal flag to block all subsequent read or write commands. In this case, the firmware returns a command error ($0B) status.

Mode Sense Command CDB

	BYTE OFFSET	VALUE	COMMENTS
0	1A	Command code
1		00	LUN is inserted into bits 7-5
2		03	Page 3, current values
3		00	Reserved
4		2C	Allocation length
5		00	Control byte: no link, no flag

The READ/WRITE command performs the following to a Winchester disk:

A-2