AN137: The X9520 in Fibre Channel/Gigabit Ethernet Applications

The X9520 in Fibre Channel/Gigabit
Ethernet Applications
®
Application Note
May 5, 2005
AN137.0
Authors: Joe Ciancio, Ali Ghiasi
Abstract
This Application Note looks at the functionality and features
of the X9520 family of devices, and gives examples of how
such devices may be used in Fibre Channel/Gigabit Ethernet
applications such as Gigabit Interface Converter (GBIC) or
“MSA” (Multisource Agreement) fiber optic modules. We will
show how the designer may use the X9520 Family of
devices in such applications in order to facilitate higher
system integration, improved manufacturing process,
smaller footprint, lower system cost and higher reliability.
Introduction
In recent years, the ever increasing bandwidth requirements
of almost all aspects of computer networking, has seen the
rapid adoption of fiber optic technology into this arena, and
has driven the volume of transceivers by several fold.
Applications such as Storage Area Networks (SAN’s) have
driven the popularity of protocols such as Fibre Channel
(FC), due to its attributes of low cost, high bandwidth, low
latency, stability and high RAS (Reliability, Availability,
Serviceability) [1]. The adoption of the Fibre Channel
physical layer (FC-PH) as a basis for the Gigabit Ethernet
(GE) (IEEE 802.3z) physical layer [2][3], has further
popularized this protocol.
Both FC and GE allow for different physical media such as
copper cable (such as Twin-ax), as well as fiber optic cable
(Multi Mode and Single Mode). The remainder of this
discussion will focus on the optical implementations of
FC-PH applications.
In order to co-ordinate the development and implementation
of FC and GE system transceivers, the Small Form Factor
(SFF) Committee (a committee comprising of a range of
Industry representatives) has defined a standard for what is
known as the Gigabit Interface Converter (GBIC) module [4].
This Multisource Agreement (MSA) group is currently in the
process of defining a new SFP (Small Form Factor,
Pluggable) GBIC module called “MSA”.
Gigabit Interface Converter (GBIC)/MSA Basics
At the simplest level, the GBIC/MSA module is a full duplex
data transceiver (Transmitter and Receiver), with two data
“ports”. One “port” is for optical data (unless the GBIC is a
copper variant), and may be realized as a Duplex SC optical
connector. This connector provides for the reliable, low loss
connection of two optic fibers to the GBIC module - one for
transmitting optical data, and one for receiving optical data.
The other “port” is dedicated for electrical signals, and may
be realized as a 20-pin SCA-2 Connector. The SCA-2
connector of the GBIC module is plugged into the host
device. The electrical signals handled over this connector
1
are module fault or alarm, transmit disable, signal detect,
module identification, as well as the electrical high speed
serial data.
Using these two data ports, the GBIC provides the
simultaneous Electrical to Optical (E/O) and Optical to
Electrical (O/E) conversion of data (Figure 1). Host devices
built with GBIC ports are flexible and capable of accepting
various optical or copper converter.
The GBIC/MSA module accepts 8B/10B encoded,
differential serial data, which complies with the FC-PH
Physical Layer. The adoption of FC-PH compliant GBIC
modules, makes them suited to not only to FC, but also to
GE systems, as well as distributed multiprocessor, processor
to peripheral, and data storage interconnect, as well as other
proprietary applications requiring high bandwidth serial links.
GBIC and MSA modules are also specified to be “Hot
Pluggable” devices. This requires that the modules may be
inserted into, or removed from the host device without
having to shut down power to device. This requirement is
important in applications such as servers, where it is
desirable to have zero down time. The Hot Pluggable nature
of the GBIC modules facilitates zero down time upgrades
and maintenance.
X9520 IN GBIC/MSA APPLICATIONS
X9520 Function Overview
The X9520 has been designed specifically with the view of
integrating many of the functions required to realize a GBIC
or MSA compliant fiber optical module. In the case of MSA
optical module, the discrete implementation of the control
logic is limited by the space available. The X9520 provides a
GBIC / MSA Module
O/E
(Optical)
High Speed Data
(Electrical)
Control,
Alarm,
ID.
(Optical)
E/O
Optical SC Connector
To Fiber Optic Cable interconnect
(Electrical)
High Speed Data
20-Pin SCA-2 Connector
To Host device
FIGURE 1. GBIC/MSA FUNCTIONAL DIAGRAM
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
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Application Note 137
The X9520 features Intersil’s Block Lock function. Once
data is written to EEPROM, the Block Lock bits of the
internal Control and Status (CONSTAT) register “lock” the
appropriate area of the memory array. A write to this area of
“locked” memory is then disabled. Changing the “wiper
position” of a DCP is also disabled in this state. The Write
Protect (WP) pin, when active, further safeguards the device
and prevents any nonvolatile write operations to the
EEPROM array and DCPs.
versatile and compact solution. The device integrates the
following functions:
• Three Digitally Controlled Potentiometers
• Power On/Low Voltage Reset with Manual Reset input
• Two supplementary Voltage Monitoring circuits with
hardware and software outputs
• Integrated 2 Kbit EEPROM
Other devices in the X9520 family (the X9521, X9522.
X9523) provide various combinations of these functions to
satisfy the designers’ specific needs.
The X9520 also provides for various voltage monitoring
functions.
Power On reset and Low Voltage reset functions are
provided for Vcc. When Vcc is applied to the X9520, the Vcc
Reset Output (V1RO) pin is held HIGH until Vcc rises above
the VTRIP0 threshold (and remains higher than VTRIP1) for
the Power On Reset delay time (tpurst). After this time, V1RO
becomes LOW. The time tpurst may be selected via software
using the CONSTAT Register, from one value of either
50ms, 100ms, 200ms or 300ms. V1RO also makes a
transition to a HIGH state, when Vcc falls below VTRIP0.
The Digitally Controlled Potentiometers (DCPs) in the device
are the equivalent to a three terminal mechanical
potentiometer. DCPs however, do not suffer from
mechanical wear, they allow for repeatable nonvolatile
“wiper position” setting, and automated digital control via the
2-Wire serial data port (SDA, SCL). Traditionally and
operator had to adjust a mechanical potentiometer while
monitoring the laser waveform for optimum response and
laser safety. The process of manufacturing GBIC or MSA
optical modules can now be automated. Through the 2 Wire
bus the laser can be set, while an optical scope monitors the
module response and power.
The Power On/Low Voltage Reset circuit also has an
associated debounced Manual Reset (MR) input pin. When
MR is asserted active (HIGH) then the V1RO output makes
RH0
WIPER
COUNTER
REGISTER
RW0
RL0
8
WP
6 - BIT
NONVOLATILE
MEMOR Y
PROTECT LOGIC
RH1
CONSTAT
SDA
SCL
DATA
REGISTER
4
COMMAND
DECODE &
CONTROL
LOGIC
WIPER
COUNTER
REGISTER
REGISTER
RW1
RL1
7 - BIT
NONVOLATILE
MEMOR Y
2 Kbit
EEPROM
ARRAY
RH2
THRESHOLD
RESET LOGIC
WIPER
COUNTER
REGISTER
RW2
RL2
MR
2
VTRIP 3
+
VTRIP 2
+
VTRIP 1
+
-
V3
V2
V1 / Vcc
8 - BIT
NONVOLATILE
MEMOR Y
V3RO
V2RO
POWER ON /
LOW VOLTAGE
RESET
GENERATION
V1RO
FIGURE 2. X9520 BLOCK DIAGRAM
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AN137.0
May 5, 2005
Application Note 137
a transition to a HIGH, until time tpurst after MR returns to its
normal (LOW) state.
be connected to the MOD_DEF(1) and MOD_DEF(2) pins of
the GBIC module respectively.
V2 and V3 are supplementary Voltage Monitor inputs which
have no reset time-out, nor manual reset associated with
them. When the input monitor voltage (V2, V3) rises above
its associated threshold voltage (VTRIP2, VTRIP3), then the
appropriate hardware reset output (V2RO, V3RO)
becomes HIGH.
The current GBIC specification (Revision 5.4) [4] states that
address of the module definition EEPROM shall be “000”.
The X9520 eliminates any external addressing pins, and
instead the EEPROM address of the device is set to “000”
internally. Other addresses are used to select and control
other internal parts of the X9520, such as the DCPs and the
CONSTAT register.
A unique feature of Intersils’ X9520, is the flexibility of being
able to re-program the values of the Voltage Monitor threshold
levels (VTRIP1 - VTRIP3). By applying the desired voltage to the
appropriate external pin (V1 / Vcc,V2,V3), it is possible to
“capture” a new analog threshold level (VTRIP1 - VTRIP3).
Also, the output status of the voltage monitor circuits (V2RO
and V3RO) may be read (from the CONSTAT register) to the
host, via the 2-Wire serial interface.
The X9520 is available in Intersils Ball Grid Array (XBGA)
packaging. This package dramatically reduces the area of
board space used when compared to discrete
implementations.
X9520 Application Example
An example of how the X9520 may be used in the design of
GBIC / MSA optical module, is shown in Figure3.
The DCP’s may be used to set various parameters in the
Laser Driver & Safety Control circuitry of the optical GBIC
module. For example, the high resolution (256 tap) DCP may
be used to set the Modulation Current (IMOD) of the Laser
Diode, while the 100 tap DCP may be used to set the Bias
Current (IB) of the Laser Diode. The lower resolution (64 tap)
DCP may be used to set the maximum optical power level of
the GBIC module (via IMAX) such that it meets relevant
safety specifications such as IEC 825-1 (and CDRH). The
IEC 825-1 standard requires Class I compliance under a
single fault. The laser driver or an external circuit monitoring
maximum laser drive current is often required. The DCP
controlling IMAX provides this feature. In another situation,
two of the DCP’s may be ganged in order to provide higher
resolution for the setting of either IB or IMOD.
The DCP’s “wiper position” may be set during the time of
manufacture using Automated Test Equipment (ATE), then
“locked” using the Block Lock bits of the CONSTAT Register.
The wiper positions are then locked in the device and cannot
be changed until the user resets these bits. The Write
Protect (WP) pin adds a further level of protection to the
device. This increases device integrity, as well as eliminating
the possibility of inadvertent or intentional tampering of the
device by the end user.
The integrated 2 Kbit EEPROM memory of the X9520 can
be used to provide module definition data for the GBIC
module to the host, as specified by Annex D of the GBIC
specification [4]. The SDA and SCL pins of the device can
3
The Voltage Monitoring capabilities can be used to realize
the various alarm and safety functions that may be
implemented in GBIC optical modules. For example (figure
3), the voltage monitor input V2 may be used to monitor
laser diode over-current (OC) using a low value shunt sense
resistor, or monitor photodiode circuit. Module over-voltage
may be monitored using a simple voltage divider circuit (R1,
R2) as the input to V3.
The voltage monitor outputs V2RO and V3RO may be
OR’ed with the V1RO output of the X9520, to produce a
output signal: V2RO+V3RO+V1RO.
This signal may be interpreted as the module “Transmitter
Fault” (TX_FAULT) alarm. This alarm signal is defined to
active HIGH [4], and therefore, in this example TX_FAULT
will be active in one of three instances:
• During power up and power down of the module
• A laser over-current condition is detected.
• A module over-voltage condition is detected.
The TX_FAULT signal may also be used to drive the laser
driver circuit enable input (EN). This would have effect of
disabling the laser diode at critical times, which may cause
damage to the laser diode.
Further, the manual reset (MR) pin may be used to force
V1RO active (HIGH). This would have the effect of disabling
the laser diode, by driving the TX_FAULT output HIGH.
Hence, the MR input may be used as the “Transmitter
Disable” (TX_DISABLE) input pin on the GBIC module.
Since the voltage monitors are circuits with independent
inputs and outputs, they may configured in a manner which
best suits the designers’ requirements. For example, instead
of using V3 as an input to monitor module over-voltage, it
may be used to perform a “level shifting” function. Some
integrated fiber optic receiver IC’s provide a “Receiver Loss”
(RX_LOS) alarm (which indicates that the received optical
power has fallen below a level that produces an acceptable
Bit Error Rate (BER)). This signal however, may have a
PECL output range and therefore would not be compatible
with the GBIC specified TTL alarm levels. The voltage
monitor function of the X9520 is well suited to providing the
required PECL to TTL level shifting.
AN137.0
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Application Note 137
Conclusion
The X9520 may be ordered with pre-programmed VTRIP
levels (VTRIP1, VTRIP2, VTRIP3) which are suited to both 3.3V
as well as “legacy“ 5V GBIC module designs. These
threshold levels however, may be re-programmed at the time
of manufacture in order to suit specific designer
requirements.
This paper has reviewed the basics of GBIC and MSA
compliant fiber optic modules, an how these devices fit into
Fibre Channel and Gigabit Ethernet applications. The X9520
from Intersil was also introduced. This device was shown to
feature the functionality which simplifies design, decreases
cost, and increases the reliability of GBIC/MSA fiber optic
modules.
One final important feature of X9520, it is designed for Hot
Pluggable applications like GBIC or MSA. The X9520
provides all the necessary GBIC power on requirement
within the digitally controlled device.
Optical
Receiver
- RX_DAT
VDDT
VDDT
VDDT
MOD_DEF(2)
R2
RW2
GND
RW1
VDDT
RW0
V2
Power
Management
X9520
WP V1 / Vcc
SDA
V3
R1
VDDR
+RX_DAT
Amplifier &
Signal
Conditioning.
GND
SCL
MR
V3RO
V2RO
Vss V1RO
GND
MOD_DEF(1)
MOD_DEF(0)
TX_DISABLE
RX_LOS
TX_FAULT
VDDR
VDDT
IMOD IB
Laser
IMAX OC EN
Laser Driver
&
+TX_DAT
- TX_DAT
Safety Control
NOTE: Pull-Up resistors are not shown for clarity.
FIGURE 3. X9520 APPLICATION EXAMPLE IN GBIC/MSA OPTICAL MODULE.
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Application Note 137
References
Sites Of Interest
1. “It’s time for a SAN Reality Check”, pp. 1 - 2, Fibre Channel
Industry Association, Available from
http://www.fcloop.org/SAN/whitepapers/realitycheck.html
2. EEE Standard 802.3, 1998 Edition, Available from
http://standards.ieee.org/
3. “Gigabit Ethernet, accelerating the standard for speed”,
Gigabit Ethernet Alliance, 1997, pg 10, Avalailable from
http://www.gigabitethernet.org/technology/whitepapers/gige_97/
4. Small Form Factor (SFF) Committee Gigabit Interface
Converter (GBIC) Specification Version 5.4 - Available
from ftp://playground.sun.com/pub/OEmod
• Intersil Inc.
http://www.intersil.com
• Sun Microsystems
http://www.sun.com
• Gigabit Ethernet Alliance
http://www.gigabit-ethernet.org/
• Fibre Channel Industry Association
http://www.fibrechannel.com/
• “Lightwave” Magazine
http://lw.pennwellnet.com/home/home.cfm
Authors
Bibliography
• Johnson, Bruce, “Single Chip Transceivers Help Facilitate
Fibre-Channel Implementation”, Computer Technology
Review, May, 1999, pp. 55.
• Travis, Bill, “Fiber battles copper for serial links”, EDN,
January 6, 2000, pp. 85 -98.
• Tolley, Bruce, “Gigabit Ethernet Comes of Age”, 3COM,
Available from
http://www.3com.com/technology/tech_net/white_papers/
• X9520 Data Sheet, Available from http://www.intersil.com
Joe Ciancio
Joe Ciancio earned a BE (Electrical) with Honours, and a
BSc (Computer) from the University of Melbourne, Australia.
At Intersil, Joe is responsible for the definition and
development of new products, focusing mainly on Intersils’
Analog and Mixed Signal product line. His main areas of
technical interest include fiber optic communications and
three dimensional optical data storage techniques.
Ali Ghiasi
Ali Ghiasi is a Senior Staff Engineer of the Communication
and Optical Technologies group at Sun Microsystems. He
earned a Ph.D. from University of Minnesota. He is
responsible for development of optical and interconnect
technologies for Sun platforms. He is an active member of
the Fiber Channel and GBIC group, Where has made
significant contributions to the definition of the GBIC and
MSA fiber optic module specification.
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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