1
S2036
OPEN FIBER CONTROL
BiCMOS PECL CLOCK GENERATOR
DEVICE SPECIFICATION
OPEN FIBER CONTROL
S2036
FEATURES
Implements redundant safety interlock for laser-
based fiber optic systems
Functionally compliant with ANSI XT311 Fibre
Channel physical standard
Enables Class 1 safety compliance for FDA,
ANSI, and IEC guidelines
Operates with the AMCC S2042/S2043, and
S2044/S2045 Fibre Channel Chipsets at 265.625,
531.25, and 1062.5 Mbit/s
On-chip ring oscillator
Ultra low power operation
28-pin SOIC package
PECL Interface
APPLICATIONS
Laser-based fiber optic systems
Medical and laboratory instrumentation
High-speed data and telecommunications
- Supercomputer
- Frame buffer
- Mainframe
- Switched networks
- Broadcast
- Mass storage/RAID
- Environments
- Workstation
Figure 1. System Block Diagram
GENERAL DESCRIPTION
The S2036 is designed specifically to implement the
Fibre Channel Open Fiber Control (OFC) system, a
redundant safety interlock feature for laser-based fi-
ber optic systems. It is functionally compliant with
the ANSI XT311 Fibre Channel physical standard
and implements the OFC system defined by that
standard, to detect when the optical link has been
disrupted and shut down the laser or reduce the opti-
cal power level. The S2036 employs effectively
redundant paths, each of which can independently
turn off the laser.
The chip meets the requirements of Class 1 safety
limits defined by FDA, ANSI, and IEC. It is fully com-
patible with AMCC's S2042/S2043 and S2044/
S2045 Fibre Channel chipsets at 265.625, 531.25,
and 1062.5 Mbit/s operation. It features low-power
operation and a 28-pin SOIC package. Figure 1 shows
the S2036 used in a typical network configuration.
Optical
RX
Optical
RX
Optical
TX
Optical
TX
S2043
or S2045
RX
S2042
or S2044
TX
S2036
Open Fiber
Control (OFC)
S2042
or S2044
TX
S2043
or S2045
RX
S2036
Open Fiber
Control (OFC)
2
S2036
OPEN FIBER CONTROL
OVERVIEW
The OFC system is an open fiber link detection and
laser control system specified in ANSI XT311 Fibre
Channel physical standard. It is used as a safety
interlock for point-to-point optical fiber links that use
semiconductor laser diodes as the optical source.
The major reason for implementing OFC is that the
optical power levels required to obtain the desired
level of system performance in Fibre Channel ex-
ceeds the Class 1 limits defined by national and
international laser safety standards, if the optical fi-
ber link between two optical ports is disconnected,
such as would occur with an opened connector or a
cut fiber. It is extremely important that requirements
for Class 1 classification are met, due to the poten-
tial for customer exposure to laser radiation.
Since it is only when an optical link is opened that a
user can be exposed to laser radiation, implement-
ing OFC allows Class 1 classification requirements
to be met, since it can detect when the link has been
disrupted and can shut down the laser or reduce the
optical power level. The S2036 complies fully with
the OFC specifications and Class 1 requirements.
Refer to the ANSI Fibre Channel standard document
for details of OFC operation.
Figure 2. Functional Block Diagram
CIRCUIT OPERATION
Whenever the fiber data link is disrupted (by a cut fiber
or a disconnected connector), the S2036 detects the
disruption and forces the transceiver into a repetitive
pulsing mode of operation with a very low duty cycle.
The link returns to normal operation only when the
device detects that the disruption has been repaired
and the proper reconnection handshake has taken
place between the two transceivers in the link.
As seen in the module block diagram in Figure 2,
two loss-of-light control paths are provided and both
must be satisfied before the laser can be activated.
Each path has a separate digital filter, state ma-
chine, and a counter. Two loss-of-light detectors
each feed a digital filter. The output of each filter is
"OR/EQUALed" to produce an interval Loss-of-Light
(LOL) signal. If the REFCKIN is too fast or too slow,
the clock detector causes the laser to be deacti-
vated. Two laser driver control outputs are
independently capable of disabling the laser drive
circuitry. They are of opposite polarity to prevent
voltage control problems from accidentally activating
the laser. The link status output signals the user
system when the link is inactive.
A power-on-reset signal is used to synchronize the
counters and state machines. Three user system
control lines, Laser Fault, Link Control and
Loopback Enable, force the S2036 to disable the
laser drive circuitry and turn off the laser.
DIGITAL
FILTER
OR/
EQL
STATE
MACHINE
AND
DE-GLITCH
AND
COUNTER
COUNTER
PULSE
REPETITION
TIMER
AND
INV
AND
INV
STATE
MACHINE
OR/
EQL
DIGITAL
FILTER
CLOCK
DETECT
LOL1
LNKCTRL
LOOPEN
CSRW
LOL2
LDENP
LDENN
OFCDEFB
OFCDEF
LNKSTAT
LOL1B
(PECL)
LASERFLT
CSSTROBE
RESET
POR
SYSTEM CLOCK
SELECT
RING
OSCILLATOR
REFCKIN
CNTRL1/CNTRL1B
CNTRL0/CNTRL0B
CNTRL2
TESTEN
PRT(2:0)
3
3
3
3
S2036
OPEN FIBER CONTROL
Symbol
Description
25 Mbyte/s
50/100 Mbyte/s
Units
CNTRL0/0B
Counter Control 0
Low
High
--
t
Pulse duration time
617
154
sec
T
Pulse repetition time
10.1
10.1
sec
t
Stop time
1234
617
sec
LDENon
LOL1 & LOL2 inactive to LDENP/N
24
24
sec
LDENoff
LOL1 or LOL2 active to LDENP/N
2040
2040
sec
ldon
Laser turnon time
LDENon + Laser activation time
--
ldoff
Laser turnoff time
LDENoff + Laser deactivation time
--
pdf1
Propagation delay, fiber 1
--
pdf2
Propagation delay, fiber 2
--
The two state machines are independent and identi-
cal, and contain the logic to detect when the optical
link becomes open due to a disconnection or break.
They also preside over the link reconnection hand-
shake when it detects that the link is reconnected.
OFC Time Periods
The OFC system uses a repetitive pulsing technique
(i.e., laser activated for t microseconds every T sec-
onds) during the time that a link is open in order to
reduce the maximum possible exposure to a value
which allows for classification as a Class 1 laser
product. The maximum average power level per
pulse is a function of the wavelength, pulse duration
(t), and pulse repetition frequency (PRF = 1/T).
To function correctly, each short-wavelength optical
link port must contain a transmitter/receiver unit that
has implemented the OFC system with compatible
OFC interface timings. The timing values that are
consistent with the stated maximum transmitter re-
ceptacle power and current (1990) IEC laser safety
restrictions for a Class 1 system are shown in Table 1.
These time periods, when used according to the
OFC interface specification described in this section,
should result in a laser product which conforms to
current (1990) emission requirements for Class 1
classification worldwide. Note, however, that classifi-
cation of a laser product must always be verified with
measurements and calculations and not assumed.
The connection and disconnection handshake timing
is shown in Figures 5 and 6. The connection hand-
shake is performed at link initialization or at the
automatic recovery from intentional or accidental in-
terruption of the optical path. The Pulse duration, t, is
chosen to meet the maximum average power level
while allowing for the propagation delay through both
fibers and the light detection and laser turn-on delay
of the complete transceiver system. This margin is
shown as t
setH
. Similarly, the Stop time t
s
is set at
either 2t or 4t to assure that the detected pulse origi-
nates from a properly functioning OFC node. This is
accomplished by the detection of loss of light for a
time t
setL
prior to the end of the Stop time. In Figure
5, the Master node is the one whose 10.1 second
timer expires first after the reconnection is complete.
Figure 6 illustrates the reaction of the system to the
disruption of one fiber (the one between the Master
transmitter and the Slave receiver). Since the other
fiber is still intact in this example, the Master trans-
mitter is shown as again having its 10.1 second
timer expire first, but then resynchronizing to the re-
ceived pulse from the Slave transmitter.
Safety Documentation/Usage Restrictions
Shortwave laser transceiver products incorporating
the OFC system in order to assure Class 1 compli-
ance shall include the following two usage
restrictions as part of the product's user, mainte-
nance, and safety documentation:
Table 1. Selectable OFC Time Periods
s
t
t
t
t
t
t
4
S2036
OPEN FIBER CONTROL
a)The laser product shall be used in point-to-point
optical links only. The OFC safety system is
incompatible with other types of link connections
(i.e., multiple input or output links). Failure to
comply with this usage restriction may result in
incorrect operation of the link and points of access
that may emit laser radiation above the limit for
Safety Class 1 systems established by one or
more national or international laser safety standards.
b)Normal operation of the point-to-point optical link
requires that the laser product shall be connected
only to another Fibre Channel compatible laser
product that includes the OFC safety system. In
addition, each of these products must be certified
as Safety Class 1 laser products according to the
laser safety regulations and/or standards in existence
at the time of manufacture.
The certification ensures that each of the products
will function correctly in the event of a fault in one of
the safety control systems.
It is the responsibility of the interface designer tassure
that the redundancy and freedom from single point
failure sensitivity incorporated in the Fibre Channel
standard and the design of the S2036 are fully
implemented in the final laser product. These imple-
mentation criteria shall include but are not limited to:
a)Biasing of the LDENP/N signal lines with 10K
resistors external to the S2036 assures that the
non-operating state of the laser is forced if the
S2036 is removed or destroyed while the system is
operating.
b)Use of the redundant control signals (CNTRL0B
and CNTRL1B) to assure safe operation or no operation
in the event of a single point failure of any control signal.
Figure 3. OFC Connections
S2044
Fiber
Channel
Transmitter
OFC
S2045
Fiber
Channel
Receiver
CNTRL (1:0)
CNTRL 1(1B:0B)
POR
LNKCTRL
REFCKIN
LOOPEN
LASERFLT
Fiber
Optic
TX
Fiber
Optic
RX
SD+:1=Light, 0=No Light
SD:1=No Light, 0=Light
+ Laser Enable
Laser Enable
Data
Loss of Signal (PECL)
SD+
SD-
Data
LOCKDETN
LOL1
LOL1B
LOL2
TCLK
LDENN
LDENP
OFCDEF
OFCDEFB
WARNING! IMPORTANT!
The S2036 is equipped with an overrride func-
tion to permit activation of the attached laser
during module level testing. This function is op-
erable with the TESTEN held in the active high
state and OFCDEF held High and OFCDEFB
held Low only. It is the responsibility of the
manufacturer to isolate these inputs from acci-
dental activation by the end user. Failure to do
so may void the certification of the module or
the OEM system for Laser Safety Class 1 op-
eration.
Digital Filter
The digital filters integrate the incoming signals to
improve their reliability. The filters sample at a faster
rate when acquiring a light-present signal and at a
slower rate when dropping a light-present signal,
while maintaining the correct handshake timing.
5
S2036
OPEN FIBER CONTROL
State Machine
The state machine is implemented per the Fibre
Channel FC-PH document, Paragraph 6.2.3 and an-
nex I. The OFC time periods are user-selectable to
comply with the operating frequency of the serial
link. The selectable OFC time periods are seen in
Table 1. The pulse repetition time is fixed for both
25, 50, and 100 Mbyte applications to 10.1 seconds.
The inputs to the state machine are the loss of light
indicators (DC and AC) and the power-on reset. The
timing of the state machine transitions is controlled
by the decode times. The timing of the laser control
signals will not necessarily be synchronous to the
system clock because of the long counter times involved.
Link Initialization
Following a power-on-reset cycle, the OFC device
will be in the Stop State as defined in the Fibre
Channel Standard. The default state for the internal
loopback control is loopback active. A Control/Status
Write cycle is required together with a logic high on
the LOOPEN input in order to place the OFC in the
Reconnect State allowing the repetitive pulsed out-
put operation. The required timing for this write cycle
is shown in Figure 5.
Reference Clock Select
The reference clock is user-selectable to be 53 MHz
or 26 MHz. The reference clock input is divided by
four if a 53-MHz clock is used, or by two for a 26-
MHz clock so that all state machine and counter
clocks operate at 13 MHz. Refer to Figure 3 and
Figures 7 through 10 for suggested connections.
Clock Detect
The clock detect circuitry compares the reference
clock input and the ring oscillator. If the ring oscilla-
tor and the reference clock frequencies do not
compare as selected by CTRL2, CTRL1/1B, and
CTRL0/0B, the laser is disabled to prevent it from
staying on or increasing the laser duty cycle.
De-Glitch Logic
The de-glitch logic debounces the power-on reset
and the link control pin to eliminate potential glitching
of the laser control lines.
Counter
The two counter blocks are redundant functions
which generate the selected decode timing used by
the state machines. (See Table 1 for OFC time peri-
ods.) One of the counters is used as the lower part
of the 10.1 sec pulse repetition timer.
Pulse Repetition Timer
The pulse repetition timer generates the 10.1 sec
decode timer used by the state machines. In test
mode it is broken up into three counter stages which
is output on the PRT<0> pin.
Figure 4. Loopback Enable Write Access
0
OFC ENABLED , 1
LASER OFF
LOOPEN
CSRW
Trwsu
Tcsmpw
Trwh
Tch
Tcsu
CSSTROBE
Symbol
Description
Min
Max
Units
Trwsu
CSRW setup time before CSSTROBE rising edge
5
ns
Trwh
CSRW hold time after CSSTROBE rising edge
5
ns
Tcsu
LOOPEN setup time before CSSTROBE rising edge
5
ns
Tch
LOOPEN hold time after CSSTROBE rising edge
5
ns
Tcsmpw
CSSTROBE minimum pulse width
15
ns
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