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Page 12
Extended messages
Parity errors
The following table lists extended SCSI messages and their definitions.
Hex Code
Message
Synchronous
01h
Data Transfer
Request
Wide Data
03h
Transfer
Request
The following table describes the operation for each of the possible cases of parity
error.
State or Phase
Bus Free State
Arbitration Phase
Selection Phase
Selection, Message Out
Phase (Identify Message)
Reselection, Message In
Phase (Identify Message)
Command Phase
Definition
The drive will never initiate a Synchronous data transfer negotia-
tion, but will expect the initiator to do so.
If the message is received after selection and before command
phase, it will then go to Message In phase and respond with a valid
response to complete the negotiation.
If the message is received at any other time, a Message Reject is
sent in response.
The drive will never initiate a Wide Data Transfer negotiation, but
will expect the initiator to do so.
If the message is received after selection and before Command
phase, it will then go to Message In phase and respond with a valid
response to complete the negotiation.
If the message is received at any other time, a Message Reject is
sent in response.
Description
The drive does not detect nor react to parity errors on the SCSI bus while
the drive is in a bus free state.
The drive does not detect nor react to parity errors on the SCSI bus while
arbitration is being performed.
The drive does not detect nor react to parity errors on the SCSI bus while
the drive is being selected.
If the drive detects a parity error while the host is sending an Identify
message, the drive retries forever.
If the drive is attempting to reconnect to the host and the host asserts
ATN because it detected an error, the drive:
♦ Switches the host to the Message Out Phase.
♦ Waits for the host to send a 09 (Parity Error Message)
♦ The drive then performs the retry option by:
♦ Switching the host to the Message In Phase.
♦ Resending the Identify Message
If the drive detects a parity error while the host is transferring a CDB, the
drive:
♦ Switches the host to Message In phase
♦ Sends Restore Data Pointers (03h) message
♦ Switches the host to Command phase to retry the command.
♦ If a parity error occurs on the retry the host:
♦ Terminates the transfer.
♦ Switches the host to the Status Phase and sends a Check Condition.
♦ Switches the host to the Message In Phase and sends a Command
Complete.
♦ Sets the Sense Key = B and ASC/ASCQ = 47-00 (SCSI-2 only).
LTO SCSI Interface Manual
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