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Chapter 5 Initiator Mode
Initiator | Page 5 - 5 |
Setting DBV,
DAT and DIR
Bits
Using the
Table Values
Note
If you set a combination of DBV, DIR and DAT that is inconsistent with how your target executes the command, you will receive error code 24H, Unexpected SCSI Phase Encountered. You must refer to your vendor- specific documentation for information about your peripheral’s command execution.
The DAT and DIR bits, together, indicate whether a data transfer should be expected for a given command, and if so, which direction it will be: to or from the target. The DBV bit gates whether the values for DAT and DIR will be derived from the default table or from the values you assign.
The following table of defaults is useful for you to use when you wish to: 1.) alter the default behavior of a standard SCSI command for a specific application or 2.) implement a
An example of altering the default function of a command can be demonstrated with the SCSI Format command. If you examine the DAT, and DIR bit values for this command in the table, you see that the adapter assumes:
Opcode | DAT | DIR | Description |
04H | 1 | 1 | Format Unit |
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Table 28: Example DAT and DIR bit settings
The ones in the table for DIR and DAT mean that by default the adapter will assume that there is data associated with the command and the direction of data flow is to the target.
If the Format command for your device requires no data transfer, set the Flags-
1 byte as follows when you issue the Format command:
DBV = 1, DAT = 0, DIR = 0.
Setting DBV to one tells the adapter to examine your settings for DIR and DAT and their zero settings indicate no data is associated with the command.
An example of the second case, implementing a
Opcode | DAT | DIR | Description |
02H | 0 | 0 | not defined |
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Table 29: DIR and DAT Settings, Vendor-unique
In this example, suppose the 02H opcode
DBV = 1; DAT = 1; DIR = 0
This combination means; DBV is set so use
User’s Guide | 21020285 D |