100 SERIES
Advanced Communications
ACS102A Fiber Modem
ACS102A Data Sheet
Features
Full duplex serial transmission over single/twin fiber.
Link lengths up to 25km.
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Supports asynchronous data rates from DC to 162kbps.
Full diagnostic modes - Remote and Local loopback.
Ultra low power consumption, typically 2-3mA, which could be
extracted from the RS-232 port for self powered applications.
Uses a single Ping Pong LED or Laser Duplex Device for single fiber
applications, low cost LED/PIN or Laser/PIN combinations for twin
fiber applications.
Additional operating mode to support PIN with integrated TIA.
Supports 3 additional low frequency asynchronous channels or
the RS-232 handshake signals.
Digital and differential voltage input modes, plus modes for non
fiber applications - RF
Bit Error Rate (BER) < 10
-9
Available in 44 pin TQFP (part no: ACS102A-TQ) and 44 pin
PLCC (part no: ACS102A-PL) packages.
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A
S
C
0
1
3B4B
Encoder
A
2
2
TRC
TxD
Digital
Filter
Data
Compress
FIFO Time
Compress
PPLED
LDD
LED/PIN
Laser/PIN
combinations
LED/Laser
Driver
LED/PIN
Receiver
RxD
Digital
Filter
Data
Decompress
FIFO Time
Decompress
3B4B
Decoder
RS-232 Interface
Control Logic
DCDB CTS
DSR RIO
RTS
DTR RII
DR(3:1) DM(3:1) HD(2:1) DP
HBT ERL PORB
Equivalent Block Diagram of ACS102A
ACS102A Revision 1.6 September 2000
Description
The ACS102A is a complete controller, driver and receiver IC, supporting full-
duplex asynchronous transmission from DC to 162kbps over a single serial link.
Although primarily designed for single optical fibre applications, any other simple
serial media may be used. The ACS102A is optimised for very low power
consumption, consuming only 2 - 3mA at RS-232 data rates including power
provided to the LED and 'heartbeat' monitor. In applications where the power is
extracted from the RS232 data lines, this leaves a generous amount of power left
for any power extraction and RS-232 level shifting circuitry.
The ACS102A employs data compression and time compression techniques,
affording high launch power in short bursts, leading to a low average power
consumption. The advantage of this approach is that high link budgets can be
achieved with inexpensive optical components.
For example, the recommended set-up for RS-232 applications (19.2kbps +
handshake signals) assumes that the LED is driven with a peak current of
approximately 15.4mA for 6 % of the time. The machine cycle is short enough to
facilitate power supply smoothing with a small external capacitor in the region of
100µF.
1
Advanced Communications
ACS102A Data Sheet
Single/Dual Fiber Modem for Asynchronous Data Rates from DC to 160kbps
Transmitter and Receiver Functions
This device offers one high speed and three low speed full duplex
channels to the user in a completely transparent way, appearing as
4 full duplex channels even though the medium connecting the
devices may only be a single fiber link.
Data from the TxD and low frequency channels is time
compressed in an internal FIFO and sent over the fiber link in a
burst within a predefined window. The device at each end of the
link automatically synchronise with each other such that the
transmit and receive windows are interleaved. The TxD input data
of the transmitting modem is also data compressed. The 3B4B
encoding method is used for communication between ACS102As,
thus ensuring that there is no DC component in the signal. The
encoding and decoding is transparent to the user.
In the receiving modem, 3B4B encoding ensures easy extraction of
the bit-clock. The received data is filtered, decoded, and then
stored in the output memory. The memory provides time expansion,
de-jittering and frequency compensation functions. The data is then
decompressed and directed to the RxD output pin, appearing after a
minimal delay, in the same format as that presented at the TxD pin
at the far end.
Mode 4 - Single Fiber 3-pin LASER/PIN mode
Setup : DP5=0, DP4=0, DP3=1, DP2=0, DP1=1
This is a single-fiber mode where the LASER is used for transmis-
sion and the monitor PIN diode within the LASER is used for
reception. Differential reception from the PIN diode is used to
maximise sensitivity. Connections are shown below :
LASER
LAP
Fiber
PINP
LAN
3-pin LASER single fiber mode
Mode 5 - Single Fiber 4-pin LASER/PIN mode
Setup : DP5=0, DP4=0, DP3=1, DP2=0, DP1=0
This is a single-fiber mode where the LASER is used for transmis-
sion and the monitor PIN diode within the LASER is used for
reception. Differential reception from the PIN diode is used to
maximise sensitivity. Connections are shown below :
2
Operational Modes
The ACS102A is compatible with the ACS102 but offers over twice
the max data rate and incorporates the laser interface modes
previously associate with the ACS402. The ACS102A is a pin and
functional compatible replacement for both the ACS102 and
ACS402. The following sections detail the operating modes for all
configurations of LED, LASER and LED/PIN or LASER/PIN
combinations. Additional modes are also described for new ways of
interfacing the device with external PIN / amplifier modules.
LED Interface Modes
Mode 1 - Single Fiber LED mode
Setup : DP5=0, DP4=0, DP3=0, DP2=1, DP1=0
This is the operational mode for single fiber transmission with a
PPLED. The LED is used for both transmission and reception of
data over the fiber. An example circuit diagram showing the
necessary connections is shown in figure 4. This also shows an
example circuit for interfacing to the RS232 voltage levels of a PC
serial port.
Mode 2 - Dual Fiber LED/PIN mode
Setup : DP5=0, DP4=0, DP3=0, DP2=1, DP1=1
This is a twin-fiber mode where the LED is used for transmission
and a separate PIN Diode is used for reception. This allows the use
of less expensive standard LEDs and PINs rather than bi-directional
PPLEDs or Duplex devices. An example circuit diagram showing
the necessary connections is shown in figure 5.
LASER Interface Modes
Mode 3 - Dual Fiber LASER/PIN mode
Setup : DP5=0, DP4=1, DP3=0, DP2=1, DP1=0
This is a twin-fiber mode where the LASER is used for transmission
and a separate PIN Diode is used for reception. An example circuit
diagram showing the necessary connections is shown in figure 6.
Differential reception from the PIN diode is used to maximise
sensitivity. Since PINP is also used for LASER current control via
monitoring of the monitor diode current, the LAP and LAN pins are
automatically floated during data reception.
Either 3 or 4 pin LASERs may be used in this mode. For 4 pin
LASERS the extra pin of the monitor diode cathode is connected
to the LASER anode, the same as it is shown in figure 6 with the
internal connection of a typical 3-pin LASER.
LASER
LAP
PINN
PINP
LAN
Fiber
4-pin LASER single fiber mode
LASER Duplex Device Use
The Laser duplex device is composed of a 3 or 4 pin Laser for
transmission and a PIN diode for reception in a single housing.
Mode 3, as detailed previously is used for interfacing to these
devices. The Duplex devices are driven by the ACS102A in a half-
duplex manner, even though to the user it appears as a full duplex
link. As a consequence potential cross-talk between the transmit-
ter and receiver is ignored, allowing excellent performance from
low cost components.
Additional Alternative Modes
The previous modes detail the most common setups for most
typical LED, LED/PIN or LASER/PIN combinations. Many other
possible operating modes are possible via the DP1-5 pins setups.
Some of the other less common connection combinations are
shown below. These include modes for using a LASER as a
receiver as well as a transmitter in a single fiber link, where the
LASER device supports this, receiving from both the LASER and
monitor PIN, and modes for digital interfacing to external PIN/
transimpedance amplifier (TIA) modules. Only use those setups
on DP1-5 indicated in this specification, other pin combinations
may activate unpublicised functional or test modes which may lead
to damage of the LASER, where this is used.
Mode 6 - Single Fiber 4-pin LASER/PIN mode (Las & mon recv)
Setup : DP5=0, DP4=0, DP3=0, DP2=0, DP1=0
This is a single-fiber mode where the LASER is used for transmis-
sion and the LASER and the monitor PIN diode within the LASER is
used for reception. Connections are as in mode 5.
2
Advanced Communications
Mode 7 - Single Fiber 3-pin LASER/PIN mode (Laser recv)
Setup : DP5=0, DP4=0, DP3=0, DP2=0, DP1=0
This is a single-fiber mode where the LASER is used for transmis-
sion and only the LASER is used for reception. Connections are as
in mode 4.
Preamp Interface modes
Mode 8 - Preamp Voltage Input & LED Drive
Setup : DP5=1, DP4=0, DP3=1, DP2=0, DP1=0, NSB=0
This is a mode for use with external amplifier and PIN modules. An
LED is used for transmission and connected as normal with its
anode to LAP and cathode to LAN. The differential voltage from an
external PIN/TIA module is connected to PINN and PINP via
100pF capacitors to provide DC isolation. The signals should be
connected such that PINP is connected to the TIA output that goes
high when light is received. A single input can also be applied from
a single ended PIN/TIA by feeding the input to PINP only, PINN is
left floating. This mode uses the new NSB pin, in all other modes
this pin should be left disconnected or connected to VA+.
Mode 9 - Preamp Voltage Input & LASER Drive
Setup : DP5=1, DP4=0, DP3=1, DP2=0, DP1=1, NSB=0
This is a mode for use with external amplifier and PIN modules. A
LASER is used for transmission and connected as normal as
described under mode 3. The differential voltage from an external
PIN/TIA module is connected to PINN and PINP via 100pF
capacitors to provide DC isolation. The signals should be
connected such that PINP is connected to the TIA output that goes
high when light is received. A single input can also be applied from
a single ended PIN/TIA by feeding the input to PINP only. With a
LASER drive the PINN and PINP inputs are also connected to the
LASER monitor diode. This may induce extra noise but should not
interfere with the operation. This mode uses the new NSB pin, in
all other modes this pin should be left disconnected or connected
to VA+.
Digital interface modes
Mode 10 - Digital Data Input & LASER Drive
Setup : DP5=0, DP4=1, DP3=1, DP2=0, DP1=0
This is a mode for use with external amplifier and PIN modules that
provide fully digital output levels. A LASER is used for transmission
and connected as normal as described under mode 3. The output
from an external PIN/TIA module is connected to CNT. The
polarity of the input should be such that CNT that goes high when
light is received.
Mode 11 - Digital Data Input & LED Drive
Setup : DP5=1, DP4=1, DP3=0, DP2=1, DP1=0
This is a mode for use with external amplifier and PIN modules that
provide fully digital output levels. An LED is used for transmission
and connected as normal as shown in figure 5. The output from an
external PIN/TIA module is connected to CNT. The polarity of the
input should be such that CNT that goes high when light is
received.
Transmit Current Control
LED current control
The LED transmit current is not critical though it is important not to
exceed the LED manufacturer's recommendation for maximum
current. The current is controlled by a resistance Rtrc connected
between TRC and GND. The lower the value of Rtrc the greater
the current. The lower limit for Rtrc is 800Ω while a practical
maximum is 40kΩ.
The LED current is inversely proportional to Rtrc while Rtrc > 800Ω.
LED current = (100 / Rtrc) +/- 25 %
LASER current control
ACS102A Data Sheet
The LASER output current must be set for each individual device
in accordance with the manufacturer’s recommendations. The
output current to the LASER is controlled by a variable resistor
(Rtrc) between TRC and ground. The lower the value of Rtrc the
greater the current. The minimum value of Rtrc is 800Ω. The
ACS102A derives and controls the average optical power being
produced by measuring the current in the LASER's monitor PIN
diode and integrating this measurement using the capacitor on the
CTX pin, which is typically 10nF. A control loop is established
which works to maintain the average optical power at a constant
level whilst parameters such as voltage, temperature and LASER
efficiencies may vary. The average optical power is always one
half of the peak power since the LASER is driven between full on
and full off, with an average mark-space ratio of 50%. An example
circuit arrangement is shown in figure 6.
Adjustment Procedure
Select the appropriate LASER drive mode using the pins DP1-5
(see section headed
Operational Modes).
The LASER drive
current and hence transmitted optical power is set by adjusting
Rtrc until the required output power is obtained, taking account of
the maximum allowed drive current set by the LASER manufac-
turer.
There are two ways of measuring the output power and drive
current, either dynamically in the normal operating mode or
statically by setting the pin SETB low.
If measuring power dynamically during the normal mode, the
output from the laser can be measured using an optical-power
meter that is capable of detecting peak optical-power. If an
averaging optical power meter is employed then a correction factor
of 16 must be used to obtain the peak value :
LASER(peak power) = Laser(average power) * 16.
To measure power statically, the SETB pin must be pulled low to
ground. This forces the device to constantly transmit through the
LASER at a fixed level. This fixed level will be equivalent to half of
the peak level, since the normal control loop within the device
works to control the average power level through integrating out
the alternating data pulses.
LASER(peak power) = Laser power(with SETB=0) * 2.
Since all currents are static in this mode, a simple optical power
meter can be used and the drive current in the laser can be easily
measured by connecting an ammeter between pin LMN and VA+.
LMN provides a convenient means of monitoring the LASER drive
current through the relationship :
LASER(current) = 100 x LMN(current)
+/- 8%.
2
Dynamic measurement of the LMN current is also possible by
connecting a resistor to LMN and measuring the voltage pulses.
Data-Rate Selection
The ACS102A benefits from data compression circuitry which
reduces power consumption and improves the BER (Bit Error
Rate). The compression technique employed, demands a
minimum TxD data-bit time of 10 sample-clocks. This defines the
maximum data rate:
Maximum data rate = sample-clock/10
However, an allowance must be made for any variation in the TxD
data-bit period to accommodate frequency variation and jitter.
Hence the maximum data rates specified in the following are
decreased by 10% to include a sufficient safety margin.
The ACS102A includes an input pulse shaper which ensures that
the system is very tolerant to jitter, and helps achieve a maximum
data-rate close to the theoretical maximum of sample-clock/10
(bps). The pulse shaper will expand data pulses of less than 10
clock-samples to meet the compression criteria. This is performed
on up to three consecutive data-bits which fail to meet the
minimum pulse width criteria.
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Advanced Communications
DR3
DR2
DR1
XTAL
Clock
10MHz
10MHz
10MHz
10MHz
10MHz
20MHz
27MHz
Sample
Clock
XTAL/160
XTAL/80
XTAL/40
XTAL/20
XTAL/15
XTAL/15
XTAL/15
Max TxD
Data Rate
5.6kbps
11kbps
22kbps
45kbps
60kbps
120kbps
162kbps
ACS102A Data Sheet
maximum frequency will not be compressed beyond the standard
CF of 1.
Super-compress mode provides benefits where the user is
interested in low average power consumption (e.g. battery life)
rather than peak power. If the intended system is idle for most of
the time with periodic bursts of activity, the additional data
compression afforded will approach a CF of 3.
Locking
To achieve low power consumption the ACS102A is active for a
small percentage of the frame (machine-cycle) known as the
'transmit' window and the 'receive' window, collectively these
windows are known as the 'active time'. Outside the 'active time'
the device is largely dormant accept for the maintenance of the
oscillator and basic 'house-keeping' functions.
Communicating modems attain a stable state known as 'locked',
where the 'transmit' window of one modem coincides with the
'receive' window of the other, allowing for the delay through the
optical link.
Adjustments to machine cycles are made
automatically during operation, to compensate for differences in
XTAL frequencies which cause loss of synchronisation.
The ACS102A locking algorithm is statistical, and consequently
the locking time will differ on each attempt to lock.
Diagnostic and Locking Modes
The diagnostic and operational modes, shown in Table 3, are
selected using the DM pins.
DM3
0
0
0
1
1
1
DM2
0
0
1
0
1
1
DM1
0
1
0
1
0
1
Mode
Full-duplex
Full-duplex
Full-duplex
Local loopback
Remote loopback
Full-duplex
Lock
Drift
Active
Memory
Random
Random
Random
0
1
1
1
1
1
1
1
0
0
1
1
1
1
1
0
1
0
1
1
1
Table 1. TxD Data-Rate Selection
Table 1. shows the maximum TxD data rate, which includes a 10%
tolerance margin, when using various frequency crystals, other
sample-clock frequencies may be generated by using the
appropriate value XTAL in combination with the divide constant
selected by DR(1:3) namely 15,20,40,80 or 160.
The advantage of using a slower crystal and a lower sample clock
is the reduced power consumption of the device.
RS-232 Handshake Signals / Low Frequency Data Channels
Three additional low frequency data channels are provided on the
ACS102A which are often used for the RS-232 handshake signals.
The RS-232 handshake signals comprise the set RTS, CTS, DTR
and DSR. These are treated as pass through data channels rather
than using local handshaking. Hence the status of inputs RTS and
DTR appear at the far-end outputs CTS and DSR respectively. An
extra data channel has also been provided, which may be used for
sending the RS232 Ring Indicator signal, for example. The input
and output lines are RII and RIO respectively.
The transmission method employed on the ACS102 has been
designed to give low skew (1 - 2 data-bits) on the main RTS, CTS,
DTR and DSR handshake signals relative to the main TxD/RxD
data channel, while maintaining low power consumption.
The handshake signals are updated by two stimuli:
i.
ii.
an internal interval timer at a frequency proportional to the
XTAL; at 10.0MHz this is approximately 1.6ms.
changes detected on RTS and DTR.
2
Table 3. Diagnostic and operational modes
Local Loopback
In local loopback mode TxD data is looped back inside the near-end
modem and appears at its own RxD output. RTS, DTR and RII are
also looped back appearing at their own CTS, DSR and RIO outputs
respectively. The data is also sent to the far-end modem and
synchronisation between the modems is maintained.
In local loopback mode data received from the far-end device is
ignored, except to maintain lock. If concurrent requests occur for
local and remote loopback, local loopback is selected.
The local loopback diagnostic mode is used to test data flow up to,
and back from, the local ACS102A and does not test the integrity of
the link itself, i.e. local loopback operates independently of
synchronisation with a second modem.
Remote Loopback
In remote loopback mode, the near-end modem sends a request to
the far-end modem to loopback its received data, thus returning the
data so that it appears at the RxD of the initiating modem. RTS,
DTR and RII follows the same path, returning data back to CTS,
DSR and RIO respectively of the initiating modem. Data also
appears at the far-end modem outputs RxD, CTS, DSR and RIO. In
the process both modems are exercised completely, as well as the
LED/PINs and the fiber optic link. The remote loopback test is
normally used to check the integrity of the entire link from the near-
end (initiating) modem. Whilst a device is responding to a request
for remote loopback from the initiating modem (far-end), requests to
initiate remote loopback will be ignored.
Drift lock
Communicating modems attain a stable state where the 'transmit'
window of one modem coincides with the 'receive' window of the
other, allowing for delay through the optical link. Adjustments to
machine cycles are made automatically during operation to
compensate for differences in XTAL frequencies which would
otherwise cause loss of synchronisation.
4
The maximum bandwidth for the handshake signals may be
programmed using pins HD(1:2) in accordance with the Table 2.
HD2
0
0
1
1
HD1
0*
1
0
1
Sampling
Frequency
600
10
5
2.5
Hz
kHz
kHz
kHz
Skew
w.r.t. RxD
10 ms.
1 - 2 data bits
1 - 2 data bits
1 - 2 data bits
Table 2. Handshake signal bandwidth allocation
* When HD2 = HD1 = 0 super-compress mode is selected. See
section headed
Super-Compress mode.
Handshake data rates which exceed the allocated bandwidth will
be delayed, and consequently result in additional skew between
handshake signals and data.
The HD pins enable the user to allocate a maximum bandwidth to
the handshake signals and thus limit the power consumption of the
device. The power consumption is, however, dependent on the
actual bandwidth used and not the bandwidth selected. For
example; if the handshake signals were toggled at 1kHz the power
consumption would be the same for an allocated bandwidth of
2.5kHz as it would for an allocation of 10kHz. See section headed
Current and Power Consumption
for more details.
Super-Compress mode
This mode is selected when HD2 = HD1 = 0. Super-compress
mode performs a second stage of data compression, thus further
reducing the power consumption of the modem. Normally, data is
compressed in a manner which is independent of the data type. In
super-compress mode, an additional stage of compression further
reduces the data by a factor of 1 to 3 depending on the data itself.
Example: The super-compress stage will compress DC data by an
additional Compression Factor (CF) of 3, whilst data close to the
Advanced Communications
Using drift lock, synchronisation described above depends on a
difference in the XTAL frequencies at each end of the link, and the
greater the difference the faster the locking. Therefore, if the
difference between XTAL frequencies is very small (a few ppm),
automatic locking may take tens of seconds or even minutes.
Drift lock will not operate if the two communicating devices are driven by
a clock derived from a single source (i.e. tolerance of 0ppm).
Active Lock Mode
Active lock mode may be used to accelerate synchronisation of a
pair of communicating modems. This mode synchronises the
modems in less than 3 seconds by adjusting the machine cycles of
the modems. Active lock reduces the machine cycle of the device
by 0.5 % ensuring rapid lock. After synchronisation the machine
cycle reverts automatically to normal.
Only one device may be configured in active lock mode at any one
time. Active lock mode is usually invoked temporarily on power-up.
This can be achieved on the ACS102A by connecting DM1 to an RC
arrangement, i.e. with the capacitor to 5V and the resistor to GND, to
create a 5V
à
0V ramp on power-up. The RC time constant should
be Ca. 5 seconds. Active lock will succeed even when
communicating devices are driven from clocks derived from a single
source (0ppm).
Random Lock
This mode achieves moderate locking times (typically 5 seconds,
worst case 10 seconds) with the advantage that the ACS102’s are
configured as peers. Communicating modems may be permanently
configured in this mode by hard wiring the DM pins.
Random lock will succeed even when communicating devices are
driven from clocks derived from a single source (0ppm). Random
lock mode is compatible with drift lock and active lock.
Memory Lock
Following the assertion of a reset (PORB = 0) communicating
devices will initiate an arbitration process where within 10 seconds
the communicating modems will achieve synchronisation with one
establishing itself as an active lock modem and the other
establishing itself as a drift lock modem. On subsequent attempts to
lock, synchronisation will be achieved within 3 seconds. It is only
necessary to apply reset to one device in the communicating pair to
initiate an arbitration process.
Since memory lock uses on-chip storage, loss of power to the
modem will require a new reset (PORB=0). Furthermore, should
there be a need to synchronise with a third modem a reset will again
be required.
Mixing Lock modes
It is possible to mix all combinations of locking modes once the
modems are locked, however, prior to synchronisation two modems
configured in active lock will not operate. The effect of mixing
locking modes on locking speed is given in Table 4 :
Device A
Mode
Drift
Drift
Drift
Drift
Active
Active
Active
Random
Random
Memory
Device B
Mode
Drift
Active
Random
Memory
Active
Random
Memory
Random
Memory
Memory
Locking Speed
Drift
Active
Random
Random
Not allowed
Random
Random
Random
Random
Active
(Random on first synchronisation)
ACS102A Data Sheet
crystal oscillator will operate with padding capacitors of value 0 -50pF,
and the designer should endeavour to use padding capacitors of low
value since this will ensure the lowest power consumption. The
ACS102A has been designed to operate with a crystal tolerance of +/
- 250ppm giving a relative tolerance between communicating modem
pairs of 500ppm. This wide tolerance will support the use of low value
padding capacitors.
Alternatively, XLI may be driven directly by an external clock. The
clock frequency for the purpose of this specification is referred to as
the XTAL frequency. The operational range for the XTAL frequency is
5 - 27MHz, though communicating devices must use the same
nominal value.
DCDB
The Data Carrier Detect (DCDB) signal goes Low when the modems
are synchronised ('locked') and ready for data transmission. Prior to
lock (DCDB = High), the data channel output RxD will be forced Low
and the handshake outputs CTS and DSR will be forced High.
The status of DCDB is also given by the HBT pin. See section headed
HBT Status pin.
CNT Capacitor
The CNT value is inversely proportional to the XTAL frequency. The
capacitor is connected between pins CNT and GND. A 20 %
tolerance on CNT is sufficient. For a XTAL frequency range of
5 to 27MHz the recommended value of the capacitor on CNT is from
47nF at 5MHz, 22nF at 10MHz down to 10nF at 27MHz . A ceramic
type is required to ensure low leakage. The CNT capacitor value has
an effect on the initial locking time and the receiver sensitivity limit.
Higher values giving improved sensitivity and lower values giving
faster locking.
ERL (Error Detector)
This signal can be used to give an indication of the quality of the
optical link. Even when a DC signal is applied to the data and
handshake inputs, the ACS102A modem transmits up to 200kbps
over the link in each direction. This control data is used to maintain
the timing and the relative positioning of 'transmit' and 'receive'
windows.
The transmit and control data is constantly monitored to make sure it
is compatible with the 3B4B format. If a coding error is detected, ERL
will go High and will remain High until reset. ERL may be reset by
asserting PORB, or by removing the fiber-optic cable from one side of
the link thereby forcing the device temporarily out of lock.
Please note that ERL detects coding errors and not data errors,
nevertheless because of the complexity of the coding rules on the
ACS102A the absence of detected errors on this pin will give a good
indication of a high quality link.
HBT Status pin ('Heartbeat' Indicator LED)
The ACS102A HBT pin affords a method of driving a display LED in a
manner which is sympathetic to low power consumption. The HBT pin
is pulsed to indicate 'locked' status (DCDB = 0) and 'out of lock' status
(DCDB =1). The frequency of pulses is 8 times greater for 'out of lock'
than for 'lock'. The LED 'on' indicates power-up whilst the frequency
of pulsing denotes locking status.
Since the display LED is on for (at most) 3.2 % of the total time, the
HBT requires little power which may be further reduced by employing
high efficiency LEDs.
Powered-up, but not locked
Frequency (Hz):
Duration (s):
On time (%):
With 10MHz XTAL :
XTAL / 3.89 * 10
6
61,440 / XTAL
3.2 % of time.
Frequency:
2.5Hz (approx.)
Duration:
6.1ms (approx.)
XTAL / 15.36 * 10
6
61,440 / XTAL
0.4 % of time.
Frequency:
0.65Hz (approx.)
Duration:
6.1 ms (approx.)
2
Table 4. Mixing lock modes
PORB
The Power-On Reset or PORB resets the device if forced Low for
100ms or more. This pin should be connected as figure 4.
Crystal Clock
Normally, a parallel resonant crystal will be connected between the
pins XLI and XLO with the appropriate padding capacitors. The
Powered-up and locked
Frequency (Hz):
Duration (s):
On time (%):
With 10MHz XTAL :
5
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