Black Box MX880A User manual

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INFORMATION
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AUGUST 1993
MX880A
MX880AE
MX880A-ST
MX880AE-ST
Async/Sync Fiber Optic Multiplexor

FEDERAL COMMUNICATIONS COMMISSION
AND
CANADIAN DEPARTMENT OF COMMUNICATIONS
RADIO FREQUENCY INTERFERENCE STATEMENTS
This equipment generates, uses, and can radiate radio frequency energy
and if not installed and used properly, that is, in strict accordance with
the manufacturer’s instructions, may cause interference to radio
communication. It has been tested and found to comply with the limits
for a Class A computing device in accordance with the specifications in
Subpart J of Part 15 of FCC rules, which are designed to provide
reasonable protection against such interference when the equipment is
operated in a commercial environment. Operation of this equipment in
a residential area is likely to cause interference, in which case the user at
his own expense will be required to take whatever measures may be
necessary to correct the interference.
Changes or modifications not expressly approved by the party
responsible for compliance could void the user’s authority to operate
the equipment.
This digital apparatus does not exceed the Class A limits for radio noise emission
from digital apparatus set out in the Radio Interference Regulation of the
Canadian Department of Communications.
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les
limites applicables aux appareils numériques de Classe A prescrites dans le
Règlement sur le brouillage radioélectrique publié par le ministère des
Communications du Canada.
TRADEMARKS USED IN THIS MANUAL
ST is a registered trademark of AT&T.
Freon is a registered trademark of E. I. du Pont de Nemours
& Company.
Any other trademarks mentioned in this manual are acknowledged
to be the property of the trademark owners.

ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
Contents
Chapter Page
1.0 Specifications ............................................................................................. 1
2.0 Introduction ............................................................................................... 3
2.1 Description .......................................................................................... 3
2.2 Applications ......................................................................................... 4
3.0 Configuration ............................................................................................. 6
3.1 Selecting the Number of Subchannels .............................................. 7
3.2 Setting Synchronous Data Rates ........................................................ 7
3.3 Selecting the Transmit Clock (TC) Source ....................................... 7
3.4 Setting the Ground ............................................................................. 8
4.0 Installation .................................................................................................. 9
4.1 AC Power Requirements ..................................................................... 9
4.2 Main Channel ...................................................................................... 9
4.3 Subchannels ...................................................................................... 10
5.0 Operation ................................................................................................. 12
5.1 Controls and Indicators .................................................................... 12
5.2 Operating Procedure ........................................................................ 13
5.3 System Tests ....................................................................................... 13
6.0 Troubleshooting ...................................................................................... 15
6.1 Front-Panel Indicators Don’t Light ................................................. 15
6.2 Local Sync Loss LED Is ON .............................................................. 15
6.3 Remote Sync Loss LED Is ON .......................................................... 16
6.4 Calling Your Supplier ....................................................................... 17
6.5 Shipping and Packaging ................................................................... 17

1
CHAPTER 1: Specifications
Approvals — FCC Class A, DOC Class/MDC classe A
Multiplexing
Technique — Time division
User Channels — (6); (12) with Doubler Cable (EYN356)
Interface — Channel: Serial EIA RS-232C/CCITT V.24, DCE;
Composite: Dual fiberoptic
Protocols — On 3 or 9 channels: Asynchronous only;
On 3 channels: Asynchronous or synchronous
(user-selectable)
Clock — Internal, external from DTE, or external from
remote modem (user-selectable)
Operating Mode — Full duplex over dual fiberoptic cable
Speeds — Channel: Asynchronous: Transparent to all speeds
up to 38,400 bps; Synchronous: 1200, 2400, 4800,
9600, or 19,200 bps (user-selectable);
Composite: 2.46 Mbps
Operating Range — 3.2 mi. (5.2 km)
Operating
Wavelength — 820 nm
Optical Output — -23 dBm minimum into 50/125 G. I. fiber;
-16 dBm minimum into 100/140 G. I. fiber
Receiver
Sensitivity — -40 dBm minimum
Dynamic Range — 24 dBm minimum
1.0 Specifications

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ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
User Controls — (8): (2) Front-mounted pushbuttons: Local Loopback,
Remote Loopback; (6) Internal: (3) Jumpers: Number
of Channels, Clock Source, Connected/Disconnected
Grounds; (3) Rotary Switches: Synchronous Data
Rate/Asynchronous for Channels 1 through 3
Indicators — (4) Front-panel LEDS: Power, Test, Local Sync Loss,
Remote Sync Loss
Diagnostics — Local and remote digital loopback
Connectors — (9) Rear-mounted: (6) DB25 female; (1) Power inlet;
Units without “-ST” suffix: (1 TX, 1 RX) SMA 905
female;
Units with “-ST” suffix: (1 TX, 1 RX) ST®female
Leads/Signals
Supported — RS-232: 1, 2, 3, 4, 5, 6, 7, 8, 15, 17, 20, 24 (PGD, TXD,
RXD, RTS, CTS, DSR, SGD, DCD, TXCLK, RXCLK,
DTR, and EXTCLK respectively)
Power — From outlet over 5-ft. (1.5-m) detachable line cord:
Consumption: 8.5 VA maximum;
For 120-VAC, 60-Hz operation:
Input range: 115 VAC ±10%, 47 to 63 Hz;
For 240-VAC, 50-Hz operation:
Input range: 230 VAC ±10%, 47 to 63 Hz
Fuse — Slo-Blo: For 120 VAC: 0.2 A; For 240 VAC: 0.1 A
Temperature — 32 to 122˚F (0 to 50˚C)
Humidity — Up to 95%, noncondensing
Size — Standalone: 1.75"H x 13.3"W x 7.9"D (4.4 x 33.8 x 20 cm)
Rackmount: 1.75"H x 19"W x 7.9"D (4.4 x 48.3 x 20 cm)
Weight — Standalone: 3.5 lb. (1.6 kg)
Rackmount: 3.85 lb. (1.75 kg)

3
CHAPTER 2: Introduction
2.1 Description
The Async/Sync Fiber Optic Multiplexor is a full-duplex time-division
synchronous/asynchronous multiplexor that enables up to 12 terminals to be
multiplexed onto a single fiberoptic channel. (The mux’s normal total of six
subchannels can be increased to 12 by using channel-doubler cables, product
code EYN356.) Channels 1 through 3 can be set to operate either synchron-
ously or asynchronously, while the remaining three or nine channels always
operate asynchronously.
Various configurations can be set up to suit your specific needs:
• Up to six asynchronous data channels with one control signal per channel
at data rates up to 19,200 bps. (A control signal is the same as hardware
flow control.) This signal, input to the local unit on Pin 14 (STXD,
Secondary Transmitted Data), is transposed at the remote unit and
output on Pin 16 (SRXD, Secondary Received Data). The control signal
may require special cabling; the mux can process it only in 6-channel (not
12-channel) mode at up to 19,200 (not more) bps.
• Up to six asynchronous data channels without control signals at rates
up to 38,400 bps. (Distortion increases at async speeds above 19,200 bps,
preventing the use of control signals.)
• Up to six data channels: up to three operating synchronously at rates
up to 19,200 bps and the rest operating asynchronously, with no control
signals, at rates up to 38,400 bps.
• Up to 12 data channels: up to three operating synchronously and the
rest operating asynchronously, with no control signals, all at rates up to
19,200 bps.
These configurations are set by adjusting the rotary switches and jumpers
located on the main board (see Chapter 3).
The unit implements asynchronous multiplexing using an over-sampling
technique. Each of the 12 channels is sampled at 76.8 kbps on the electrical
side while on the optical side the rate of sampling is doubled. Table 2-1 on the
next page summarizes the unit’s performance in its various configurations.
2.0 Introduction

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ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
2.2 Applications
The primary application of the Async/Sync Fiber Optic Multiplexor is for
point-to-point configurations where distances of up to several kilometers are
involved. For example, where a cluster of terminals is connected to a host
computer through a single link, as in Figure 2-1 below:
Table 2-1. Performance in Various Configurations
Total # of Max. # Subchannels Data Rate Distortion (%) Controls per
Subchannels In Use (kbps) (Async Channels) Subchannel
Sync Async Sync Async
6 3 6 minus sync 19.2 19.2 6.25 0
6 3 6 minus sync 19.2 38.4 12.5 0
6 3 6 minus sync 19.2 19.2 12.5 1
12 3 12 minus sync 19.2 19.2 12.5 0
NOTE: To reduce async distortion, operate the multiplexor in the 6-channel mode, at no more
than 19,200 bps, whenever possible. There is no distortion on sync channels in any mode.
Figure 2-1. Typical point-to-point installation.
HOST

5
CHAPTER 2: Introduction
For installations involving clusters of terminals distributed in several
locations, the Async/Sync Fiber Optic Multiplexor units may be installed
in a ring-type (multipoint) arrangement, as shown below in Figure 2-2.
Figure 2-2. Typical ring (multipoint) installation.
On each terminal-end mux in a ring arrangement, the unconnected channels
must be bypassed by shorting Pin 2 to Pin 3 of the relevant subchannels’
connectors. During synchronous operation, if a bypass is needed for a given
unit’s Channel 1, 2, or 3, the transmit-clock source in that unit should be set
to “received clock” (RX; see Section 3.3). Not more than two adjacent units
should operate in the RX mode.

6
ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
Four setup procedures must be completed before the multiplexor can
be installed and operated: selecting the number of subchannels, setting
synchronous data rates, selecting the transmit clock (TC) source, and setting
the ground. Refer to the board layout in Figure 3-1, below, for the location
of the straps (jumpers) and switches referred to in the rest of this chapter.
3.0 Configuration
Figure 3-1. Internal strap and switch locations.

7
CHAPTER 3: Configuration
3.1 Selecting the Number of Subchannels
1. Unscrew the two upper-cover screws located at the back of the unit and
slide the upper cover backward.
2. Locate the strap labeled “SELECT 6 OR 12 CHANNELS.”
3. For up to 6 channels with no controls, place the strap between the center
pin and the one marked “6.” For any other application, place the strap
between the center pin and the one marked “12.”
3.2 Setting Synchronous Data Rates
1. With the cover off the multiplexor, locate the three rotary data-rate
switches marked “CH.1,” “CH.2,” and “CH.3,” and the rate table located
to the left of these switches.
2. If you want to operate Channel 1, 2, or 3 in the synchronous mode, you
must rotate the channel switch(es) to the appropriate data-rate setting(s)
(refer to the rate table). If the synchronous mode isn’t needed, set the
three switches to positions 5, 6, or 7 (asynchronous mode).
3.3 Selecting the Transmit Clock (TC) Source (Synchronous Operation Only)
1. With the cover still off the multiplexor, locate the strap marked “TC
SOURCE.”
2. For normal synchronous operation (the Transmit-Clock signal is
generated internally), place the strap over the “IN” column of pins.
For loopback timing (the TC is synchronized to the Received-Clock signal
from the remote modem), place the strap over the “RX” column of pins.
If an External-Clock signal is provided by a DTE device on RS-232 Pin 24,
place the strap over the “EX” column of pins. Only Channel 1 can accept
an External Clock.

8
ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
3.4 Setting the Ground
1. With the cover still off the multiplexor, locate the strap marked “GND.”
According to your requirements, set the signal ground to either be
connected to or disconnected from the shielding (chassis or protective)
ground.
2. Slide the multiplexor cover back into place and fasten the screws.

9
CHAPTER 4: Installation
4.1 AC Power Requirements
AC power is supplied to the Async/Sync Fiber Optic Multiplexor through a
5-foot (1.5-meter) cord terminated by a grounded three-wire plug; therefore,
the multiplexor must be placed within five feet of a grounded AC outlet. The
AC cord is fused at the rear-panel AC-power receptacle of the unit. A 0.l-A
Slo-Blo fuse is required for 230-VAC operation and a 0.2-A fuse is required
for 115-VAC operation.
4.2 Main Channel
1. Remove the protective caps from the two fiberoptic connectors (“RX” and
“TX”) on the rear panel of the multiplexor (see Figure 4-1, below) and
keep them in a safe place for later use.
2. Apply Freon®spray to both connectors to clean the optical surfaces, which
may be coated with dust from shipping.
3. Connect the transmitting fiber to the connector marked “TX” and the
receiving fiber to the connector marked “RX.” If the connectors are SMA
type, secure the fastening nuts tightly.
4. At the remote unit, the transmitting fiber must be connected to the “RX”
connector and the receiving fiber to the “TX” connector.
4.0 Installation
Figure 4-1. The rear panel of a 230-VAC unit.

10
ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
4.3 Subchannels
Six DB25 female connectors, located on the rear panel, enable the end-users
to be connected to the unit. Detailed information about the signals present
at these connectors is given in Table 4-1 on the next page. To operate the
multiplexor with more than six channels, channel doublers are required
(see Figure 4-2, below).
Figure 4-2. Connecting a channel-doubler cable to a subchannel.

11
CHAPTER 4: Installation
CCITT EIA Pin # Signal Name Description
V.24 R5-232-C
101 AA 1 Protective Ground Chassis ground. Can be isolated from
Signal Ground.
102 AB 7 Signal Ground Common signal- and DC-power-supply
ground.
103 BA 2 (14) Transmit Data Serial digital data input from a terminal
or other source to the multiplexor.
104 BB 3 (16) Receive Data Serial digital data output from the mux.
105 CA 4 (19) Request to Send A positive level to the mux when the
DTE wants the mux to transmit data.
Inside the mux, this pin is tied to Pin 5.
106 CB 5 (13) Clear to Send A positive level from the mux if it can
transmit data. Inside the mux, this pin
is tied to Pin 4; the mux “reflects” RTS
back to the DTE without delay.
107 CC 6 (21) Data Set Ready A positive DC voltage (+8V) from the
mux indicating the unit is powered.
108.2 CD 20 (25) Data Terminal Ready Pinned but not functional.
109 CF 8 (12) Receive Line A positive level from the mux except
Signal Detector when either a sync loss occurs or
(Carrier Detect) remote loopback is performed.
9 +8V These signals are reserved for data-set
10 -8V testing and for powering mini modems.
113 DA 24 External Clock Available only for Channel 1. Clock
input from a terminal or other source
to the mux for synchronous
transmission.
114 DB 15 Transmit Clock Available only for Channels 1 to 3.
Clock output from the mux for
synchronous transmission.
115 DD 17 Received Clock Available only for Channels 1 to 3.
Clock output from the mux for
synchronous reception.
NOTE: Pin numbers in parentheses represent secondary channels available when you use
a channel-doubler cable.
Table 4-1. Pin Assignments for Subchannel Connectors

12
ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
The installation procedures covered in the previous section must be
completed and checked before the multiplexor can be operated properly.
5.1 Controls and Indicators
This section describes the front-panel controls and indicators (shown in
Figure 5-1, below).
5.0 Operation
Figure 5-1. Front-panel controls and indicators.
5.1.1 C ONTROLS
• Local Loopback (LLB) Button: Press to perform local loopback test.
• Remote Loopback (RLB) Button: Press to perform remote loopback test.
NOTE: If both buttons are pressed simultaneously, the action will be
disregarded by the multiplexor and normal operation will continue.
5.1.2 I NDICATORS
• Power: Green LED lights when power is ON.
• Test: Yellow LED lights when either the local or remote unit is
performing a test.
• Local Sync Loss: Red LED lights when synchronization is lost at the local
unit.
• Remote Sync Loss: Red LED lights when synchronization is lost at the
remote unit.

13
CHAPTER 5: Operation
5.2 Operating Procedure
CAUTION!
The protective-ground terminals of the multiplexor must be connected to
the protective-ground conductor of the power cord. The mux’s power-
cord plug should be inserted only in (a) an outlet provided with a
protective-ground contact or (b) an extension cord with a protective-
ground conductor; any type of power connection that doesn’t provide
grounding leaves the mux defenseless.
1. Plug the multiplexor’s AC power cord into an AC outlet. The Power
LED will light up to indicate that the mux is ON. If the local and
remote muxes are both operating and their main channels are properly
connected with fiberoptic cable, no other LED should be ON. If other
LEDs light up, please refer to Chapter 6.
2. To turn off the mux, simply remove its power cord from the outlet.
5.3 System Tests
The multiplexor performs two system tests: local loopback and remote
loopback.
5.3.1 L OCAL L OOPBACK
When the mux performs local loopback, the data from the local transmitter
is looped back to the local receiver at the digital level, which checks all local
digital circuitry for proper operation.
To activate the local loopback test, press the “LLB” pushbutton located
on the front panel of the multiplexor (see Figure 5-1). If the local unit is
operating properly, the yellow Test LED should be lit and all other LEDs
should be off.
Furthermore, if the local and remote units are properly connected across
their main channels, the yellow Test LED on the remote unit should be lit
too, which indicates that a check of the local transmitter’s analog interface
and both the analog and digital remote receiver’s sections is being
performed.

14
ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
5.3.2 R EMOTE L OOPBACK
Remote loopback sends data back from the remote receiver to the remote
transmitter, which checks all local digital circuitry as well as both the local
and remote analog interfaces, main channel link, and remote digital receiver
section.
To activate the remote loopback test, press the “RLB” pushbutton located
on the front panel of the multiplexor (see Figure 5-1). If both the local and
remote units are operating properly, the yellow Test LEDs should be lit on
both units and all other LEDs should be off.
NOTE: When either the local or remote loopback test is performed, the
following signals at the remote unit’s subchannels are OFF (negative voltage):
• Receive Data (Circuit 104)
• Clear to Send (Circuit 106)
• Receive Line Signal Detector (Circuit 109)

15
CHAPTER 6: Troubleshooting
This chapter lists some problems that might occur during installation and
operation of your mux, along with some possible solutions.
CAUTION!
These service instructions are for use by qualified personnel only.
To avoid shock, do not perform any service action not listed below.
6.1 Front-Panel Indicators Don’t Light
1. Make sure power is being supplied to the unit. If the outlet the mux
is plugged into does work, and the power cord shows no signs of being
broken:
2. Try replacing the mux’s fuse. If this doesn’t help:
3. The fault might be in the unit’s power-supply circuits. Call your supplier.
6.2 Local Sync Loss LED Is ON
1. Push the “LLB” button on the mux’s front panel to trigger its local
loopback test. If the Test LED comes ON and the Local Sync Loss LED
goes OFF, go to Step 2. If this doesn’t happen, try replacing the local
unit:
A) If you don’t have a replacement unit, call your supplier.
B) If the system works fine with the replacement unit, the original local
unit is probably faulty. Send it to your supplier for repair.
C) If the system doesn’t work even with the replacement unit, go to
Step 2.
2. Push the “RLB” button on the mux’s front panel to trigger its remote
6.0 Troubleshooting

16
ASYNC/SYNC FIBER OPTIC MULTIPLEXOR
loopback test. If the Test LED comes ON and the Local Sync Loss LED
goes OFF, go to Step 3. If this doesn’t happen, try replacing the remote
unit:
A) If you don’t have a replacement unit, call your supplier.
B) If the system works fine with the replacement unit, the original remote
unit is probably faulty. Send it to your supplier for repair.
C) If the system doesn’t work even with the replacement unit, go to
Step 3.
3. Perform Steps 1 and 2 at the remote site (run the loopback tests from the
remote modem). If the fault is still not located, try replacing both the
remote and local units one at a time (if you haven’t done this already):
A) If you don’t have a replacement unit, call your supplier.
B) If the system works fine with one or the other replacement unit,
the original unit is probably faulty. Send it to your supplier for repair.
C) If the system still doesn’t work, the main-channel fiberoptic link
between the units might be broken or defective and should be checked.
If replacing the fiber cable doesn’t work, call your supplier.
6.3 Remote Sync Loss LED Is ON
Follow the same procedure as that for the Local Sync Loss problem,
but starting at the remote site.

17
CHAPTER 6: Troubleshooting
6.4 Calling Your Supplier
If you determine that your multiplexor itself is malfunctioning, do not
attempt to alter or repair the unit. Contact your supplier.
Before you do, make a record of the history of the problem. Your supplier
will be able to provide more efficient and accurate assistance if you have a
complete description, including:
• the nature and duration of the problem.
• when the problem occurs.
• the components involved in the problem.
• any particular application that, when used, appears to create the problem
or make it worse.
6.5 Shipping and Packaging
If you need to transport or ship your multiplexor:
• Package it carefully. We recommend that you use the original container.
• If you are shipping the multiplexor for repair, make sure you include its
power cord. If you are returning the multiplexor, make sure you include
its cord and this manual. Before you ship, contact your supplier to get a
Return Materials Authorization (RMA) number.