SEL Compatibility

Elliott, Robert (Hou) Robert.Elliott at
Wed Mar 1 11:19:18 PST 2000

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Hou)" <Robert.Elliott at>
This looks okay for the expanders with which I am familiar.  They may not
pass through SEL changes during data phase, but they won't be confused by it
or cause any errors.  Like you mentioned, this is only an issue for an old
expander that is snooping traffic between other devices; Ultra 320 won't be
negotiated successfully between two devices separated by a pre-Ultra 320 old

PC: Robert.Elliott at
UNIX: relliott at

> -----Original Message-----
> From: Gene_Milligan at
> [mailto:Gene_Milligan at]
> Sent: Tuesday, February 29, 2000 2:41 PM
> To: t10 at
> Subject: SEL Compatibility
> * From the T10 Reflector (t10 at, posted by:
> * Gene_Milligan at
> *
> I understand that during the SPI-4 working group there was a 
> proposal to
> initiate training with the assertion of SEL. I assume the 
> proposal was to do
> this only during data phases and I also assume only when 
> certain modes have been
> negotiated.
> This led me to look at SEL to see if there were any backward 
> compatibility
> issues. It appears there are not if new devices have their 
> protocol automation
> designed fresh for SPI-4 and that prior devices are not 
> snooping the bus (e.g.
> QAS from SPI-3).
> But what about our old unspecified nemesis - expanders. SPI-3 
> and prior states
> <<The SCSI bus phases are defined such that the SCSI bus is 
> never in more than
> one phase at any given time. In the following descriptions, 
> signals that are not
> mentioned shall not be asserted.>> Except for Arbitration, 
> Selection and Message
> with QAS phases SEL is not mentioned. Therefore I assume 
> designers could have
> detected a protocol error if SEL popped up in some other 
> phase. But for the
> prior designs what phase are the other phases in, in 
> particular the data phase,
> if SEL pops up? Except with broken new hardware/firmware I 
> assume the issue will
> not occur except in the eyes of an expander. Does someone 
> know what all
> expanders will do or at least the bulk of expander designs?
> Gene
> *
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