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ATAPI Interface Chapter 5
STT20000A Product Manual Page 57
Request Sense command
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation code (03h)
1 Reserved
2 Reserved
3 Reserved
4 Allocation Length
5 Reserved
An Allocation Length value of 20 will return all Request Sense data.
The Request Sense command is always accepted, regardless of the state of the
DSC bit, but the status is valid only when DSC or CHK (error) is set (1). If DSC and
CHK are both reset (0), a non-error “null” status is returned. Normally, if CHK is set,
DSC is set. The only time CHK is set and DSC is reset, is during writes at logical
end of media; DSC remains a buffer indicator, and CHK is set to indicate EOM,
which is a warning, not an error.
If a command completes with a check (error) condition, the next command issued, if
not Request Sense or Inquiry, will be aborted, and a deferred error will be reported.
If the command is Request Sense, a non-deferred error is reported. The Inquiry
command does not affect status reporting.
The following table describes the REQUEST SENSE layout.
Byte Description Value Meaning
0 Valid, Error Code 70h,71h 80h = Information Field Valid
+ 70h = Current Errors
or 71h = Deferred Errors
1 Reserved (Segment Number) 00 —
2 Filemark, EOM, ILI, Sense Key NN 80h = Filemark
+ 40h = EOM
+ 20h = ILI
+ Sense Key