Save Data Pointer questions

Fri Mar 7 09:06:18 PST 1997

* From the SCSI Reflector (scsi at, posted by:
* KD6NNM at
>  According to the SCSI-2 rev. H copy of the standard, section 5.6.6 2nd
>  seems to say there SHALL (on disconnecting devices) be a SAVE DATA POINTER
>  DISCONNECT message after each successful connection (except possibly the 
>  last).  This would say that after the command phase there should be one.
>  one is to look at what the message 02 SAVE DATA POINTER message does, it 
>  only saves the DATA POINTER not the COMMAND or STATUS pointer, section 
>  5.6.20, so it does not make sense for a target to do a 0204 sequence after

>  the COMMAND phase, but that's not what the standard says.  Generally you 
>  don't see the SAVE DATA POINTER after
>  the COMMAND phase, but it seems I have seen this before.  Because there is

>  an implied RESTORE pointer message on a reconnect, the COMMAND and STATUS 
>  (and DATA) pointers are restored to the last saved values, so there is not
>  need to do the SAVE DATA pointer message after the COMMAND phase, but SCSI

>  standard does say SHALL send 0204 sequence after all successful
>   Your call.

I agree with Jim.  I would also "sum it up" as follows:

"When DATA moves --- SAVE DA (DATA) POINTERS!"

"If DATA has NOT moved --- Save or don't.  Results are the same.

Greg A.

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