IBM Ultrastar 36LZX Specifications page 198

If after the Target's response above the Initiator asserts the ATN signal and the first message received is
either a Message Parity Error or a Message Reject message, the Target negates the data transfer width
agreement and goes to 8 bits mode. For the Message Parity Error case the implied data transfer width
agreement is reinstated if the Target successfully retransmits the Wide Data Transfer Request message
to the Initiator. For any other message the Target completes negotiation and goes to the negotiated data
transfer width.
10.1.3.2 Transfer Width Negotiation started by the Target
If the Target recognizes that negotiation is required, the Target sends a Wide Data Transfer Request
message to the Initiator with the transfer width exponent equal to 1 (E = 01h). The Initiator must respond
by asserting the ATN signal prior to its release of ACK for the REQ/ACK handshake of the last byte of
the Wide Data Transfer Request message. This provides an interlock during the wide data transfer
negotiation. If the Initiator does not assert the ATN signal, the Target goes to 8 bit mode. If the Initiator
does assert the ATN signal, the Target changes to the Message Out phase and receives a message from
the Initiator.
If the first message received is a Wide Data Transfer Request message, the Target establishes the new
data transfer mode. The drive interprets the Initiator corresponding transfer width exponent as shown in
the following table.
Initiator Request
Ei = 00h
Ei = 01h
Ei > 01h
Figure 174. Target Request to Initiator
Note: If the corresponding transfer width exponent received from the Initiator indicates a data transfer
width that is greater than 16 bits (E > 01h), the Target sends a Message Reject message to the initiator
to indicate 8 bit data transfer mode.
If the first message received from the Initiator is either a Message Parity Error or a Message Reject
message, the Target goes to 8 bit data transfer mode. In the case of a Message Parity Error, the wide
data transfer negotiation is restarted if the Target successfully retransmits the Wide Data Transfer
Request message to the Initiator.
If the first message received from the Initiator is any other message, the Target goes to 8 bit data trans-
fer mode. The Target assumes that the Initiator does not support wide data transfer and does not attempt
to renegotiate with this Initiator.
The implied agreement for wide data transfer operation is not considered to exist by the Target until the
Target leaves the Message Out phase, implying that no parity error was detected. If the Target detects a
parity error while attempting to receive the message from the Initiator, the Target goes to 8 bit data
transfer mode. The Target will attempt to resume the wide data transfer negotiation by retrying the
Message Out phase.
Note: If during the Message In phase of negotiations, either Target or Initiator started, ATN is asserted
prior to transmission of the last byte of the message and the message is not Message Parity or Message
Reject, the Target goes to 8 bit data transfer mode.
Target Data Transfer Width
8 Bit Data Transfers
16 Bit Data Transfers
Send Message Reject (8 Bit Data Transfer)
Ultrastar 36LZX hard disk drive specifications
198