User's Guide

Page 20 DDS-4 SCSI Interface Manual, Rev. B
Hex
Code Message Definition
0Bh
Linked
Command
complete
with Flag
This message is sent from the DAT drive to inform an
Initiator that execution of a linked command with the Flag
bit set to one, is completed and that status was sent. The
Initiator then sets the current pointers to the initial state of
the next linked command. Typically, this message is used
to cause an interrupt in the Initiator between two linked
commands.
0Ch
Bus Device
Reset
This message is sent from an Initiator to direct the drive to
clear all current commands; it forces the drive to an initial
state with no operations pending for any Initiator. On
recognizing this message, the drive moves to the Bus Free
Phase. All modes are reset to the default state.
Identify
(80h
disable
Disconnect
/
Reconnect)
(C0h
enable
Disconnect
/
Reconnect)
These messages are sent by either the Initiator or DAT
drive to establish the physical path between them. The
physical path connection indicates that both the Initiator
and DAT drive have message passing capability. Bit 7 is
set to one to distinguish these messages from other
messages. Bit 6 is set to one by the Initiator indicating the
Initiator has the ability to accommodate disconnection and
reconnection. Bits 5 through 3 are reserved (set to zero).
Bits 2 through 0 specify the logical unit number that must
be 0 for the DAT drive. When Identify is sent from the drive
to an Initiator during reconnection, an implied Restore
Pointers message is performed by the Initiator prior to
completion of this message.
The following table describes the operation for each of the possible cases of parity
error.
State or Phase Description
Bus Free State
The drive does not detect nor react to parity errors on the
SCSI bus while the drive is in a bus free state.
Arbitration Phase
The drive does not detect nor react to parity errors on the
SCSI bus while arbitration is being performed.
Selection Phase
The drive does not detect nor react to parity errors on the
SCSI bus while the drive is being selected.
Selection, Message
Out Phase (Identify
Message)
If the drive detects a parity error while the host is sending
an Identify message, the drive will attempt one retry then
go to Bus Free.
Reselection,
Message In Phase
(Identify Message)
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