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CDU~541
CD-ROM DRIVE SCSI INTERFACE MANUAL
DISCONNECT O4H.
This message is sent from the controller to inform an
initiator that the present physical path is going to be broken (the target
plans to disconnect by releasing BSY) , but that a later reconnect will be
required in order to complete the current operation.
This message shall not
cause the initiator to save the data pointer.
After successfully sending this
message in, the controller will go to the BUS FREE phase by releasing BSY. The
controller will consider the message transmission to be successful when it
detects the negation of ACK for the DISCONNECT message with the ATN signal
false.
If DISCONNECT messages are used to break a long data transfer
into two or more shorter transfers, then a SAVE DATA POINTER will be issued
before each DISCONNECT message.
This message may also be sent from an initiator to the controller to
instruct the controller to disconnect from the SCSI bus.
After the DISCONNECT
message is received, the controller will switch to MESSAGE IN phase, send the
DISCONNECT message to the initiator preceded by SAVE DATA POINTER message, and
then disconnect by releasing BSY.
After releasing BSY, the controller will
not partiCipate in another ARBITRATION phase for at least a disconnection
delay.
If the controller cannot disconnect at the time when it receives the
DISCONNECT message from the initiator, it will respond by sending MESSAGE
REJECT message to the initiator.
INITIATOR DETECTED ERROR OSh. This message is sent from an initiator to
inform the controller that an error (e.g., parity error) has occurred that
does not preclude the
controll~r
from retrying the operation.
Although
present pointer integrity is not assured, a RESTORE POINTERS message or a
disconnect followed by a reconnect, shall cause the pointers to be restored to
their defined prior state.
ABORT 06h.
This message is sent from the initiator to the controller to
clear the present operation.
If a logical unit has been identified, all
pending data and status for the issuing initiator from the affected logical
unit will be cleared, and the controller will go to the BUS FREE phase.
Pending data and status for other initiators is not cleared.
If a logical
unit has not been identified, the controller will
go
to the BUS FREE phase.
No status or ending message will be sent for the operation.
It is not an
error to issue this message to an logical unit that is not currently
performing an operation for the initiator.
MESSAGE REJECT 07b.
This message is sent from either the initiator or
controller to indicate that the last message it received was inappropriate or
has not been implemented.
In order to indicate its intentions of sending this message, the initiator
shall assert the ATN signal prior to its release of ACK for the REQ/ACK
handshake of the message that is to be rejected.
If the target receives this
message under any other circumstance, it shall reject this message.
When the controller sends this message, it will change to MESSAGE IN phase
and send this message prior to requesting additional message bytes from the
initiator.
This provides an interlock so that the initiator can determine
which message is rejected.
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