Fujitsu M2488 manual Buffered Mode Values, Block Descriptor Field Description

M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS

	Table 4-46. Buffered Mode Values
BUFFERED	DESCRIPTION
MODE
0h	Target does not report a GOOD status on WRITE commands until the data blocks are actually written on
	the medium.
1h	The Target may report GOOD status on WRITE commands as soon as all of the data specified in the
	WRITE command has been transferred to the buffer. Write data from multiple initiators can reside in the
	buffer prior to writing the data to the medium (default).
2h	The Target may report GOOD status on WRITE commands as soon as all of the write data has successfully
	transferred to the target’s buffer from any one initiator prior to writing the block(s) to the medium. If an ini-
	tiator issued a WRITE command while the buffer contains write data from a different initiator, the target
	writes any buffered data to the medium prior to accepting any data from the new initiator.
3h -7h	Reserved

Block Descriptor:

A Block Descriptor Length of 0 indicates no block descriptors are included in the parameter list. This condition is not considered an error. The block descriptor length does not include the length of the pages.

The block descriptor specifies the medium characteristics for all of a logical unit. The block descriptor contains the Density Code, number of blocks, and block length fields.

Table 4-47. Block Descriptor

							BITS
BYTES	7	6	5		4			3	2	1	0
0						Density Code
1-3				Number of Blocks = 000000h
4							Reserved
5-7						Block Length

Table 4-48. Block Descriptor Field Description

BYTE	BIT	VALUE		DESCRIPTION
0	0-3			Density Codes of 00h and 09h write tapes in the format described by ANSI
				standard X3B5/94-043 (36-track), and read tapes in the formats described
				by ANSI standard X3B5/94-043 (36-track), X3.180-1990 (18-track) and
				X3.224.1992 (18-track extended). A Density Code of 7Fh indicates the
				Density Code is not changed. Any other code specification is rejected with
				a CHECK CONDITION status with the sense key set to ILLEGAL
				REQUEST, and the additional sense key set to INVALID FIELD IN
				PARAMETER LIST.
				NOTE: Since the ANSI SCSI-2 Standard does not define a 36-track for-
				mat, we use Density Code 09h to represent the 36-track format.
				Density Code 28h is described in Chapter 5.
1-3			0	The Number of Blocks field must contain 0. This indicates that all of the
				remaining logical blocks of the logical unit have the medium characteris-
				tics specified by the block descriptor unless a subsequent MODE SELECT
				command changes those parameters.

April 1997 CG00000-011503 REV. A 4-53