Revision 4.1
May 23, 2005
Confidential
VSC7173 Data Sheet
Enhanced 2:1 Port Selector and 1:2 Port Multiplier for Serial ATA and Serial Attached SCSI
F
EATURES
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A
PPLICATIONS
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2:1 port selector and 1:2 port multiplier for both
Serial ATA (SATA) and Serial Attached SCSI
(SAS) links
Serial ATA 1.0 compliant at 1.5 Gbps
(3.0 Gbps capable)
Passes Serial ATA patterns transparently
Programmable receiver sensitivity
High output swing mode with pre-emphasis
Compatible with VSC7175 and VSC7177 designs
0.7 W power dissipation
3.3 V power supply
32-pin, 7 mm x 7 mm QFP-N package
Active-passive redundant failover systems
Dual-port Serial ATA and Serial Attached SCSI
disk arrays (JBODs)
NAS servers
RAID subsystems
Disk-based backup systems
Serial ATA and Serial Attached SCSI routing
applications
Buffers for externally connected links
Serial ATA port replicators
Serial ATA Host Bus Adapters selecting between
internal and external connectors
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To order the VSC7173 device, see
“Ordering Information,”
page 17.
G
ENERAL
D
ESCRIPTION
The VSC7173 is a Serial ATA and Serial Attached SCSI multiplexer and buffer that implements a 2:1 port selector
function for 1.5 Gbps and 3.0 Gbps links. This function is used when dual hosts, such as I/O controllers, must access
single-port disk drives in high availability storage subsystems where redundancy and load sharing are important. The
outputs from the I/O controllers are multiplexed to a Serial ATA or Serial Attached SCSI drive. The output from the
Serial ATA drive is buffered and replicated to the I/O controllers. When switching from one I/O controller to the
other, a Serial ATA link must be re-initialized with out-of-band (OOB) signals, which are transferred through the
VSC7173 transparently. The VSC7173 provides high output swings with pre-emphasis, and programmable receiver
sensitivity that are needed to drive long backplanes and external cables.
In addition to the above features, the VSC7173 also supports a 1:2 port multiplier mode where one host can connect
two drives.
Port connectivity for the device is configured by driving external I/O pins. See the block diagram on
page 2.
Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
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VSC7173
Data Sheet
VSC7173 Block Diagram
Port 0
P0INP
P0INN
OOBPORT0
0
P0OUTP
P0OUTN
En
1 S
OOB
0
1 S
Port 2
P2OUTP
En
P2OUTN
P2INP
OOB
P2INN
Port 1
P1INP
P1INN
OOB
0
P1OUTP
P1OUTN
En
MODE1
1 S
Edge-Triggered
Logic
0
P0SLTD
S 1
MODE1
MODE0
PORTSEL0 PORTSEL1
SET
RST
Q
QN
OOBSEL [0:1]
HIV [0:2]
I/O Configuration
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Confidential
VSC7173
Data Sheet
Application Examples
The VSC7173 allows two Serial ATA hosts to access one Serial ATA drive.
Figure 1
shows a common application
where redundant I/O controllers in disk arrays have multiplexed access to single-port Serial ATA disk drives.
VSC7173
I/O Controller A
I/O Controller B
Serial ATA Drive
(1 of n)
Backplane
"Tailgate" Board
Figure 1. Serial ATA Backplane Application
Another application example (Figure
2)
is for simple port replication to enable an existing Serial ATA Host Bus
Adapter (HBA) to connect to two ports. By using the VSC7173, a single channel from the HBA may be selectively
connected to an internal connector or an external connector. The VSC7173 provides both the mulitplexing
functionality and buffering to drive external connections.
Serial ATA
Host Bus Adaptor
Port A
Internal
Connector
VSC7173
External
Connector
PCI Bus
Port B
External
Connector
Port Multiplier
Figure 2. Port Multiplier Application
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Revision 4.1
May 23, 2005
VSC7173
Data Sheet
F
UNCTIONAL
D
ESCRIPTIONS
Modes of Operation
Table 1
summarizes the VSC7173 operational mode choices. The mode of the VSC7173 is determined by the
following pins.
MODE1:
Controls whether the selection of port 0 to port 1 is edge-sensitive or level-sensitive. When LOW, port
selection is level-sensitive (to enable level-sensitive port selection, pin PORTSEL1 must also be LOW). When HIGH,
port selection is edge-sensitive.
MODE0:
Controls the function of the unselected port. When LOW, the output of this port is turned off. When HIGH,
the output of this unselected port is the same data as seen on the selected port.
PORTSEL0:
In level-sensitive mode (MODE1 is LOW and PORTSEL1 is LOW), controls the selection of port 0 or
port 1. When LOW, port 0 is selected; when HIGH, port 1 is selected. In edge-sensitive mode (MODE1 is HIGH),
controls the selection of port 0; a rising edge on this pin selects port 0.
PORTSEL1:
In level-sensitive mode (MODE1 is LOW), must be held LOW. In edge-sensitive mode (MODE1 is
HIGH), controls the selection of port 1; a rising edge on this pin selects port 1.
Table 1. Port Selection Operating Modes
Input Pins
MODE1
0 (level)
0 (level)
0 (level)
0 (level)
1 (edge)
1 (edge)
1 (edge)
1 (edge)
MODE0
0
0
1
1
0
0
1
1
PORTSEL0
0
1
0
1
X
↑
X
↑
PORTSEL1
0
0
0
0
↑
X
↑
X
P2IN
OFF
P2IN
P2IN
OFF
P2IN
P2IN
P2IN
High-Speed Connections
P0OUT
P1OUT
OFF
P2IN
P2IN
P2IN
P2IN
OFF
P2IN
P2IN
P2OUT
P0IN
P1IN
P0IN
P1IN
P1IN
P0IN
P1IN
P0IN
X = don’t care;
↑
= rising.
Status Pins
Two output pins, P0SLTD and OOBPORT0, are provided for status monitoring.
Table 2
summarizes the functionality
of these two output pins. OOBPORT0 reports whether the signal on port 0 is above or below the threshold selected in
Table 5.
P0SLTD, depending on the state of MODE1, can either report which port is selected or can report whether
the signal on port 1 is above or below the threshold selected in
Table 5.
Table 2. Output Status Pins
Input Pins
MODE1
0 (level)
PORTSEL0
X
PORTSEL1
X
P0SLTD
OOB status port 1—1 indicates signal is
below OOB threshold, 0 indicates signal
is above OOB threshold
Indicates port selected, 0 = port 1
Indicates port selected, 1 = port 0
Output Status Pins
OOBPORT0
OOB status port 0—1 indicates signal
is below OOB threshold, 0 indicates
signal is above OOB threshold
OOB status port 0
OOB status port 0
1 (edge)
1 (edge)
X
↑
↑
X
X = don’t care;
↑
= rising.
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VSC7173
Data Sheet
Reset State
The power-up state of the VSC7173 is based on the PORTSEL0 and PORTSEL1 input signals. When in level-
sensitive mode, the active port connected to port 2 is controlled directly by the PORTSEL0 input. This is the same
behavior as the normal operating condition described above. When in edge-sensitive mode, the active port connected
to port 2 is defined in
Table 3.
The state diagram in
Figure 3
indicates the same result in a different format.
Table 3. Power-up State (Edge-Sensitive Mode)
PORTSEL0
0
1
0
1
PORTSEL1
0
0
1
1
Active Port
Port 0 selected
Port 0 selected
Port 1 selected
Port 0 selected
P0SLTD Output
1
1
0
1
Reset=1
Reset State
Reset=1
(PORTSEL0=1, PORTSEL1=1
or PORTSEL1=0)
and Reset=0
PORTSEL0
PORTSEL0=0, PORTSEL1=1
and Reset=0
Port 0 Selected
PORTSEL1
Port 1 Selected
Figure 3. Reset State Machine (Edge-Sensitive Mode)
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