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21020285 D User’s Guide
Chapter 7 Board-control Commands
Page 7 - 48 Extended Unit Options (18H)
Unit Flags
The Unit Flags field of the Extended Unit Options Parameter Block is where
you can define command operation for the unit. With bit settings you can
address the issues of: synchronous data transfer, tagged commands, and use of
ATN signal.
Note
If you set the TAG flag
(explained on next page)
the adapter will ignore
the UNQ bit. Setting the
TAG bit implies that you
are using a SCSI-2 or
SCSI-3 device. The
UNQ bit is intended for
SCSI-1 devices.
UNQ Untagged Queuing - The SCSI-1 specification allows issue of
multiple, simultaneous, commands to a target that has multiple LUN’s, one
command per LUN. This bit allows you to select whether the RF3880 will
queue commands to a target with multiple LUN’s.
0 ⇒ Send one command at a time to this target.
1 ⇒ Queue commands to this target; it has multiple LUN’s.
SYN Synchronous Negotiation - Either the initiator or the target may
introduce negotiation for synchronous operation. How you set this bit
determines whether the RF3880 adapter will attempt to negotiate with the
device. Even if you do not set this bit to allow negotiation, if the other device
begins negotiation, the adapter will respond.
0 ⇒ Do not initiate negotiation for synchronous data transfer.
1 ⇒ Negotiate for synchronous data transfer.
IAT Inhibit ATN Signal - With this bit you can select whether the adapter
will assert the ATN signal during selection of a target. (Some older SCSI
devices do not respond to the ATN signal and may stop executing if it is
asserted.) Setting this bit will prevent the adapter from negotiating for
synchronous transfers, wide transfers, and SCSI-2 and SCSI-3 features. If you
enable any of these features with this bit set, you will get errors.
0 ⇒ ATN will be asserted.
1 ⇒ ATN will not be asserted during target selection.
WID Wide Transfers - Either the initiator or the target may introduce
negotiation for wide data transfers. How you set this bit determines whether
the RF3880 adapter will attempt to negotiate with the device. (Even if you do
not set this bit to allow negotiation, if the other device begins negotiation, the
adapter will respond.)
0 ⇒ Do not initiate negotiation for wide data transfer
1 ⇒ Negotiate for wide data transfer.
BITS
76543210
0 TAG 0 0 WID IAT SYN UNQ
Table 106: Unit Flags of Extended Unit Options