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21020285 D User’s Guide
Chapter 7 Board-control Commands
Page 7 - 22 Unit Options (08H)
If more than 32 bytes of sequential sense information is requested, the count
will be set to 8 and error code A1H will be returned.Otherwise, the value you
place in the Sense Count field is used in conjunction with the Selected Sense
Bytes fields. There are three ways you can use the Sense Count and Selected
Sense Bytes fields to get the result you want:
To receive the default — first eight bytes of Request Sense Data:
• Place a zero value in Sense Count field.
• Place zeroes in all fields of Selected Sense Bytes.
To receive any eight bytes of Request Sense Data from the possible 256:
• Place a zero in the Sense Count field.
• Place a number in each of the eight fields of the Selected Sense Bytes, in
the order desired.
To receive any number of the first 32 bytes of Request Sense Data:
• Place the number desired in the Sense Count field.
• Selected Sense Bytes fields are ignored.
If you wish to hand-pick more than eight bytes of Request Sense Data to be
returned in a specific order, you must use the Extended Unit Options command;
with it you can specify up to sixteen selected Request Sense bytes.
Command Code
The command code for this command is 08H.
Selected Sense Bytes
This part of the Unit Options Parameter Block is a combination of eight fields,
each containing the byte number of one of 256 possible SCSI Sense bytes.
These fields are only valid when the value of the Sense Count field of this
command is zero.
If the Sense Count field contains a 0 and all eight fields that make up the
Selected Sense Bytes field are set to 0, the default Sense bytes are returned
The default Sense bytes are bytes 0 to 7. Returned in a Status Block, they would
appear as shown below.
Byte Memory Address
Offset + 0 Offset + 1 Offset + 2 Offset + 3
Command Identifier
Reserved SCSI Status Error Flags
0 = Class/Code 1 = Segment 2 = SCSI Flags 3 = Info Byte
4 = Info Byte 5 = Info Byte 6 = Info Byte 7 = Ex Length
Table 77: Default Ordering of Sense Bytes