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PDF VSC7177 Data sheet ( Hoja de datos )

Número de pieza VSC7177
Descripción Enhanced 2:1 Port Selector
Fabricantes Maxim Integrated Products 
Logotipo Maxim Integrated Products Logotipo



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Revision 4.2
July 29, 2005
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VSC7177 Data Sheet
Enhanced 2:1 Port Selector for Serial ATA and Serial Attached SCSI
FEATURES
2:1 port selector for both Serial ATA (SATA) and
Serial Attached SCSI (SAS) links
Serial ATA 1.0 compliant at 1.5 Gbps
(3.0 Gbps capable)
Sideband port selection
Complies with Serial ATA II: Port Selector
specification 1.0, including failover control
Passes Serial ATA patterns transparently
Programmable receiver sensitivity
High output swing mode with pre-emphasis
Compatible with legacy designs (VSC7173 and
VSC7175); provides enhanced connectivity and
signal pre-emphasis
0.6 W to 0.8 W power dissipation (depending on
operating mode)
3.3 V power supply
32-pin, 7 mm x 7 mm QFP-N package
APPLICATIONS
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
To order the VSC7177 device, see “Ordering Information,” page 24.
GENERAL DESCRIPTION
The VSC7177 is a Serial ATA and Serial Attached SCSI multiplexer/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
VSC7177 transparently. The VSC7177 provides high output swings, pre-emphasis, and programmable receiver
sensitivity that are needed to drive long backplanes and external cables.
Port connectivity for the device can be configured using driving external I/O pins or through protocol-based port. 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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FUNCTIONAL DESCRIPTIONS
Modes of Operation
The VSC7177 has two modes of operation: sideband port selection and protocol port selection. Each mode
corresponds to a different method of configuring port connectivity. Only one of the operating modes is active at any
time in the VSC7177. Sideband-based port connectivity is controlled externally using the I/O pins of the device itself.
Protocol-based connectivity is implemented as defined in the Serial ATA II: Port Selector 1.0 specification.
Selecting Operating Modes
There are two types of sideband-based port selections: Edge-sensitive and level-sensitive. Rising-edge transitions on
the PORTSEL0 and PORTSEL1 inputs cause the corresponding port to become active when in edge-sensitive
sideband-based selection mode. Edge-sensitive sideband port selection is enabled when MODE1 is HIGH.
PORTSEL0 determines the active port in level-sensitive sideband-based mode. Level-sensitive sideband port
selection is enabled when MODE1 is LOW and PORTSEL1 is LOW.
Setting MODE1 LOW and PORTSEL1 HIGH in the VSC7177 allows the protocol-based Serial ATA II port selection
and test modes to be enabled. PORTSEL0 and MODE0 are used to select these operating modes shown in Table 1.
The functionality of the various operating modes is described in the following sections.
The setting of PORTSEL1 constitutes one of the primary differences between the VSC7177 and the VSC7173 and the
VSC7175. In the VSC7177, PORTSEL1 must be set LOW in level-sensitive sideband mode. The setting of
PORTSEL1 has no effect on the operation of the VSC7173 and the VSC7175 in level-sensitive mode (it is a “don’t
care”). For a complete list of differences between the VSC7177 and the VSC7173 and the VSC7175, see “Pinout
Differences Between VSC7177 and VSC7173/VSC7175,” page 13.
Table 1 shows how to configure the VSC7177 to operate in any of the various available modes.
Table 1. Operating Modes
Modes of Operation
Edge-sensitive sideband port selection
Level-sensitive sideband port selection
Reserved
Test modes
Protocol-based Serial ATA II port
selection
Test modes
MODE1
1
0
0
0
0
0
Configuration Pins
MODE0
PORTSEL0
PORTSEL1
Select output mode of
unconnected port
Select output mode of
unconnected port
edge makes port 0 edge makes port 1
active
active
Selects connected port
0 (1)
0 01
0 11
1 01
1 11
X = don’t care; = rising.
1. PORTSEL1 must equal VSS in level-sensitive sideband-based port selection mode. (The VSC7173 and the VSC7175 allow
PORTSEL1 = X.)
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VSC7177
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Output Amplitude and Pre-Emphasis
The output buffers each have an amplitude control input pin (HIV0, HIV1, and HIV2 corresponding to port 0, port 1,
and port 2, respectively) that sets the differential output voltage to normal Serial ATA levels. See Table 6.
Recommended output AC-coupling capacitor values are 0.01 µF. When the amplitude control pin is HIGH, the output
is configured for high voltage swing mode, which is useful for driving extended length media such as backplanes or
external cables. Setting the output to high swing mode should be done only in controlled environments because the
output voltage exceeds the Serial ATA 1.0 differential mode specifications.
The output buffers have a pre-emphasis circuit that is enabled when HIVx is HIGH. Pre-emphasis accentuates higher
frequency signals in a transmitted data stream. This feature takes into consideration that a signal loses amplitude and
affects the data eye opening as it goes through long trace length runs. Figure 5 shows the effects of the pre-emphasis
feature. The amplitude increase is between 20% and 30%, and the duration of the amplitude increase is between
150 ps and 300 ps.
Table 6. Output Amplitude and Pre-Emphasis
HIVx
0
1
Output Swing Level
Normal
HIGH
Pre-Emphasis
None
Enabled
Pre-Emphasis Disabled
Pre-Emphasis Enabled
VOUT
001 11 1 1 010
VOUT
0 01 1 1 1 1 0 1 0
Figure 5. Pre-Emphasis Diagram
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