Seagate Ultra 160, Ultra 320 manual Control field Bit Byte Last, Naca a, Link b

Table 62: Control field

Bit	7	6	5	4	3	2	1	0
Byte
Last	VENDOR-SPECIFIC			Reserved		NACA [a]	Obsolete	LINK [b]
							[c]	0 or 1

[a]The Normal Auto Contingent Allegiance (NACA) bit is used to control the rules for handling an Auto Contingent Allegiance (ACA) condition caused by the command. Section 7.6.1.1 specifies the actions to be taken by the logical unit in response to an ACA condition for NACA bit values of one or zero. All drives implement support for the NACA value of zero and may support the NACA value of one. The ability to support an NACA value of one is indicated in standard INQUIRY data. See Seagate SCSI Command Reference Manual, Part number 100293068.

If the NACA bit is set to a value that is not supported, the drive completes the command with a status of Check Condition and a sense key of ILLEGAL REQUEST. The procedure for handling the result- ing ACA condition operates in accordance with the supported bit value.

[b]The Link bit allows the drive to continue the task across multiple commands. Support for the Link bit is a logical unit option. A Link bit of one indicates that the initiator requests continuation of the task across two or more SCSI commands. If the Link bit is one and if the command completes success- fully, a drive that supports the Link bit continues the task and returns a status of Intermediate or Inter- mediate–Condition Met and a service response of LINKED COMMAND COMPLETE message (see Section 4.3.6). The drive completes the command with a status of Check Condition and a sense key of ILLEGAL REQUEST if the Link bit is set to one and the drive does not support linked commands.

[c]Obsolete bit. Bit 0 provides an obsolete way to request interrupts between linked commands. If bit 0 is equal to one, device servers not implementing the obsolete capability (Link bit was formerly in this bit position and Flag bit was in bit 1 position) terminate the command with CHECK CONDITION sta- tus and the sense key shall be set to ILLEGAL REQUEST.

[8]The Encryption Identification field indicates whether CDB bytes 8 through n and/or the data bytes are encrypted. The value also indicates which encryption key to use for decryption. A value of zero indicates no encryption. All other values are reserved.

[9]The Additional CDB Length field indicates the number of additional CDB bytes. This value in the Addi- tional CDB Length field shall be a multiple of 4.

[10]Service Action specific fields. The Service Action field indicates the action being requested by the applica- tion client. The Service Action field is required in the variable length CDB format and is described in Note [2]. Each service action code description defines a number of service action specific fields that are needed for that service action. If the device server detects an error during decryption of encrypted CDB bytes, it shall return CHECK CONDITION status with an additional sense code of CDB Decryption Error. If the device server detects an error during decryption of encrypted data bytes, it shall return CHECK CON- DITION status with an additional sense code of Data Decryption Error.

Parallel SCSI Interface Product Manual, Rev. A 137