Chapter 5 Initiator Mode Pass-through Commands

Initiator Pass-through Parameter Block Format

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 vendor-unique command.

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

 

 

 

 

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 vendor-unique command, can also be given. Suppose your SCSI device has a vendor-unique command available for Opcode 02H. When you examine the table for the default settings of that opcode you see that the RF3880 adapter assumes:

Opcode

DAT

DIR

Description

02H

0

0

not defined

 

 

 

 

Table 29: DIR and DAT Settings, Vendor-unique

In this example, suppose the 02H opcode vendor-unique command involves a data transfer from the device to the adapter. To override the table values and use the opcode for a vendor-unique command set the DBV, DAT and DIR bits of the Flags-1 byte as follows:

DBV = 1; DAT = 1; DIR = 0

This combination means; DBV is set so use Flags-1 field values for DAT and DIR; DAT is set so data will be transferred; DIR is zero so direction of transfer is from the device.

User’s Guide

21020285 D

Page 89
Image 89
Ciprico Rimfire 3880 manual Setting DBV DAT and DIR Bits Using Table Values, Example DAT and DIR bit settings