Fujitsu M2488 manual Identify code 80h-FFh, Ignore Wide Residue code 23h, Byte Value Description

M2488 PRODUCT GUIDE SCSI MESSAGES

If, following an initiator's responding WDTR message, the target shifts to MESSAGE IN phase and the first message in is MESSAGE REJECT, the implied agreement shall be considered to be negated and both devices shall go to eight-bit data transfer mode for data transfers between the two devices.

The implied transfer width agreement shall remain in effect until a BUS DEVICE RESET mes- sage is received, until a hard reset condition occurs, or until one of the two SCSI devices elects to modify the agreement. The default data transfer width is eight-bit data transfer mode. The default data transfer mode is entered at power on, after a BUS DEVICE RESET message, or after a hard reset condition.

Note: we recommend testing at INQUIRY DATA byte seven (07h) bits six and 5 (60h) to deter- mine if the M2488 has an installed 16 bit interface (20h) and, therefore, supports WDTR with a transfer width of 01h (16 bits). If the 16 bit interface is not installed. Then negotiation for 16 bits is not recommended, since the negotiation will be rejected and a significant performance impact is likely.

3-2.6 IDENTIFY code 80h-FFh

These messages are sent by either the initiator or the target to establish the physical path connection between an initiator and target for a particular logical unit. The logical unit number addresses one of up to eight physical or virtual devices attached to a target.

Bit 7	This bit is set to one to distinguish an IDENTIFY message from other messages.
Bit 6	This bit is only set to one by the initiator to grant the target the privilege of disconnecting. If
	this bit is zero, the target does not disconnect. This bit is set to zero if sent by the target. Refer-
	ence sections 8-6 ERROR RECOVERY PROCEDURES and 4-4 COMMAND DISCON-
	NECTION for additional information on this bit.
Bit 5	LUNTAR = 0 to specify target LUN in bits 2-0.
Bits 4-3	Reserved.
Bits 2-0	These bits specify a LUN in a target.

Only one logical unit number is identified for any one selection sequence; a second IDENTIFY mes- sage with a new logical unit number is not issued before the bus is released (BUS FREE phase). The initiator may send one or more IDENTIFY messages during a selection sequence. However, the logi- cal unit number in any additional IDENTIFY messages is the same as the logical unit number speci- fied in the first IDENTIFY message sent by the initiator.

When sent from a target to an initiator during reconnection, an implied RESTORE POINTERS mes- sage is performed by the initiator prior to completion of this message.

3-2.7 IGNORE WIDE RESIDUE code 23h

BYTE	VALUE	DESCRIPTION
0	23h	Message Code
1	01h, 02h, 03h	Ignore

This message is sent from a target to an initiator to indicate the number of valid bytes sent during the last REQ/ACK handshake and REQB/ACKB handshake of a DATA IN phase is less than the negoti- ated transfer width. The ignore field indicates the number of invalid data bytes transferred. This mes- sage is sent immediately following that DATA IN phase and prior to any other messages. The ignore field is defined in Table 3-2.

April 1997 CG00000-011503 REV. A 3-7