Ciprico Rimfire 3880 manual VME Memory Address, Transfer Count, Scsi Command Descriptor Block

	Chapter 5 Initiator Mode Pass-through Commands
Page 5 - 10	Initiator Pass-through Parameter Block Format

IAD Inhibit Automatic Disconnect - If you enable SCSI disconnect privilege with the DIS bit of the General Options Board-control command (Bit 0 of Select Flags field), disconnects will automatically be tried for any command. Use the IAD bit to disable SCSI device disconnect/reconnect privilege for the current command. This can be important for performance reasons.

0 ⇒ Determine disconnect from the DIS bit of General Options command.

1 ⇒ Ignore DIS bit, inhibit the disconnect privilege.

JSM Just Send Message - Use this bit to change the Initiator Pass-through Command Parameter Block to a Pass-through Message Parameter Block. In this Message mode, the adapter selects a device and only sends a message. This provides a measure of error recovery at the host level.

0 ⇒ Pass-through command operation as usual.

1 ⇒ Use the Pass-through Message Parameter Block format.

This message-only format is illustrated on page 5 - 11, following the description of the Pass-through command structure.

VME Memory Address

When the SCSI operation involves a data transfer, this field contains the beginning address for the transfer. Note: transfers must be word-aligned.

If the SCSI command you are issuing does not require a data transfer, the adapter ignores this field and the Address Modifier field.

Transfer Count

This field determines the number of bytes that will be transferred to or from host memory. For some SCSI commands this is an indeterminate number. In that case, there are two ways to use this field:

1.You can place a value in the field to represent the maximum number of bytes the adapter may transfer. Then, if the target attempts to transfer more data than this, the adapter will discontinue the operation and return a Status Block.

2.Alternately, you could place a zero value in this field. This causes the adapter to continue to accept data transfer requests from the target until command is complete.

SCSI Command Descriptor Block

These 12 bytes of the Initiator Pass-through Parameter Block are reserved for the actual SCSI command that will be passed to the drive. Except for the first byte, which contains the command opcode, each SCSI command uses the bytes for a different purpose; see a SCSI specification or vendor-supplied peripheral documentation for details about the commands and fields.

SCSI commands may be 6, 10, or 12 bytes in length. Any of the 12 bytes reserved for the SCSI command that are unused are ignored. The SCSI command block is passed to the SCSI device exactly as presented. The RF3880 adapter doesn’t alter any of the fields you set up.

21020285 D User’s Guide