BMQ and ATAPI bridging

Rod Wideman rod.wideman at
Mon Mar 22 08:50:51 PST 2004

* From the T10 Reflector (t10 at, posted by:
* "Rod Wideman" <rod.wideman at>

I'll take a shot at your questions.

1.  Your device should have the option of returning a check condition
for invalid combinations of BUS MODE and BMQ (e.g., a bus mode of HVD
and BMQ of 11b).  If your device does not support bus termination, it
could reject a request to drive DIFFSENS in LVD mode as well.  I see
that the ADC standard does not currently describe this, so a proposal is
welcome (from anyone).

2.  The ADC standard currently only provides port descriptors for FC and
parallel SCSI port types in this mode page.  A bridged device having a
different native interface would not provide these descriptors (unless
it was able to represent them as its own perhaps).  So, ADC currently
only addresses FC and SPI devices (not ATAPI, not SAS, etc).

Rod Wideman

-----Original Message-----
From: owner-t10 at [mailto:owner-t10 at] On Behalf Of David
Sent: Thursday, March 18, 2004 1:22 PM
To: t10 at
Subject: ADI: BMQ and ATAPI bridging

* From the T10 Reflector (t10 at, posted by:
* "David Hawks" <Hawks at>
I have a couple of ADI questions:

Table 36 of document 1558-D Revision 6 (ADC) discusses the effect of the
"bus mode qualifier" field.  This field seems to direct the target port
to drive or not drive the DIFFSENS line.  According to document 1365D
revision 10 (SPI-4), terminators drive this line, not devices.  How am I
supposed to interpret the "bus mode qualifier" field if my LVD device
does not have an internal terminator?  Can I safely ignore this field?

Consider an ATAPI device connected through a SCSI bridge.  Suppose the
ATAPI device cannot control parameters such as "minimum transfer period"
and bus mode.  Also suppose the ATAPI device cannot determine the
current transfer period or bus mode.  Does the specification allow for
such a device?  How does such a device respond when asked to change or
report said parameters?

Thank You,
David Hawks
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