Seagate STT8000A manual Request Sense command

ATAPI InterfaceChapter 5

Request Sense command

Bit	7	6	5	4		3	2	1	0
Byte
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.

STT8000A Product Manual Page 55