Emulex MD21/S2, Техническое руководство

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SCSI Bus Interface
(Busy)
(Select)
(Control/Data)
(Input/Output)
(Request)
(Acknowledge)
(Attention)
(Message)
(Reset)
-BSY f -
i i
"Bus settle delay”
-SEL f .
-I/O
f-
-REQ ( -
-ACK ( -
-ATN f—
-M S G f“
-RST f -
(Databit) D B (7 -0 ,P )f-
-( ( “
Write peripheral device
1st CMD b yte -
I —
Last CMD byte
Target “ requests”
command from
Initiator.
: COMMAND PHASE ;
The Target asserts,
C/D and deasserts I/O
and MSG for all of the
handshakes of this
phase.
The transfer is from
Initiator to Target.
HANDSHAKE
PROCEDURE:
The Target asserts
REQ. The Initiator
drives data (7-0,P) to
their desired values,
waits at least one
deskew delay plus a
cable skew delay, and
asserts ACK. The
Initiator continues to
drive data (7-0,P) until
REQ is false.
When ACK is true at
the Target, the Target
reads the data (7-0,P),
then asserts REQ.
When REQ becomes
false at the Initiator,
the Initiator may
change or release data
(7-0,P) and deassert
ACK.
The Target continues
requesting command
bytes. The number of
bytes depends on the
command group code
detected from the first
command byte
received.
-((-
First d a ta ' Last d a ta '
(read peripheral) (read peripheral)
Target “ requests” data
transfer with Initiator
DATA PHASE;
DATA IN PHASE: Read Peripheral.
L
Data is to be sent from Target to
Initiator.
- Target asserts I/O, deasserts C/D, and
MSG during the REQ/ACK handshake of
this phase.
- HANDSHAKE PROCEDURE:
The Target first drives data (7-0,P) to
their desired values, waits at least one
deskew delay plus a cable skew delay,
then asserts REQ. Data (7-0,P) shall
remain valid until ACK is true at the
Target.
- The Initiator shall read data (7-0,P) after
REQ is true, then asserts ACK.
- When ACK becomes true at the Target,
the Target may change or release data
(7-0,P) and deassert REQ.
After REQ is false, the Initiator deasserts
ACK. After ACK is false, the Target may
continue the transfer by drawing data
(7-0,P) and asserting REQ.
DATA OUT PHASE: Write Peripheral.
Data is to be sent from Initiator to
Target.
Target deasserts C/D, I/O and MSG
during the REQ/ACK handshake of this
phase. Refer to the handshake
procedure of the Command Phase.
-(L
- ( H
MD2103-0588B
Figure 7-3. SCSI Bus Timing Diagram (Sheet 2 of 3)
Interfaces
7 - 1 .1