Wide Data Transfer Request (01,02,03H) - IBM Ultrastar 36LZX Specifications

10.1.3 WIDE DATA TRANSFER REQUEST (01,02,03H)

A pair of Wide Data Transfer Request messages is exchanged between an Initiator and a Target to
establish a data transfer width agreement between the two devices. The Initiator may initiate a wide data
transfer negotiation at any time after the LUN has been identified. The Target initiates a wide data trans-
fer negotiation if the Target has not negotiated with the Initiator since the last time the Target was Reset
(Power-on Reset, SCSI Bus Hard Reset, or Bus Device Reset message).
Target-initiated negotiation occurs either immediately following the Command phase or immediately
following the first reconnection. In either case negotiation occurs before any Data phase between the
Target and the Initiator. The Target will negotiate the data transfer width agreement prior to negotiating
the synchronous data transfer agreement. If a synchronous data transfer agreement is in effect when a
Wide Data Transfer Request message is received, the Target will reset the synchronous agreement to
asynchronous mode.
The implied data transfer width agreement remains in effect until the Target is Reset (Power-on Reset,
SCSI Bus "hard" Reset, or Bus Device Reset message) or a new data transfer width agreement is
negotiated. If a Reset occurs, the Target goes to eight bit mode.
Byte Value Description
0 01H Extended message
1 02H Extended message length
2 03H WIDE DATA TRANSFER REQUEST code
3 E Transfer width exponent
Figure 172. Wide Data Transfer Request.
E The Transfer Width Exponent (E) is two to the transfer width exponent bytes wide. Valid data
transfer widths are 8 bits (E = 00h) and 16 bits (E = 01h). Value of E greater than 01h are
reserved.
10.1.3.1 Transfer Width Negotiation started by the Initiator
If the Initiator recognizes that negotiation is required and sends a Wide Data Transfer Request message
out, the Target responds by changing to the Message In phase and sending a Wide Data Transfer Re-
quest message in to the Initiator prior to transferring any additional message bytes (or any other Inform-
ation phase bytes) from the Initiator. This provides an interlock during the data transfer width negotiation.
The drive responds to each Initiator requested transfer width exponent as shown in the following table.
Initiator Target
Request Response
Ei = 00h Et = 00h
Ei > 00h Et = 01h
Figure 173. Initiator Request/Target Response
Target Data
Transfer Width
8 Bit Data Transfers
16 Bit Data Transfers
Ultrastar 36LZX hard disk drive specifications
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