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21020285 D User’s Guide
Chapter 4 Command Operation
Page 4 - 16 Some Example Single Commands
SCSI 6 byte Command Descriptor Block - These six bytes of command
information are explained in the SCSI specification.
3. Fill in the Interrupt Word of the Single command Structure. The
Interrupt Word is used for the Single Command Interrupt Level.
In this example we'll use an interrupt level of 3, and designate a Status/
ID of 3FH. This means that the adapter will interrupt the Host when the
command has completed by driving IRQ3. When requested for its
Status/ID during the VME interrupt cycle, the adapter will respond with
the value 3FH on lines D0-D7.
In memory, the structure will look like this:
Figure 16 Single Command Structure in memory
4. The next step is to load the Address Buffer Port. This will require three
writes to the port address:
Control Field = 84H - For the first write, the Control Field, we'll
select no byte or word swapping of control structures, but choose to use
a 32-bit system bus.
Address Modifier = 3DH - This is the Address Modifier that the
adapter is to use when reading the Single Command Structure.
Single Command Structure Address = 822F4H - The other two
writes to the port contain the address of the Single Command Structure.
5. The example board is jumpered at address EE00H. The three writes to
the Address Buffer Port at address EE00H will be as follows:
1.) 843DH
2.) 0008H
3.) 22F4H