Black Box MX035A User manual

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INFORMATION
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NOVEMBER 1993
MX035A MX035A-ST
MX035AE MX035AE-ST
MX036A MX036A-ST
MX036AE MX036AE-ST
RS-232 to Fiber Optic Multiplexor
RS-232 FIBER MUX-16
SDCD POWER

FEDERAL COMMUNICATIONS COMMISSION
AND
INDUSTRY CANADA
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 Industry Canada
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 Industrie Canada.
TRADEMARKS USED IN THIS MANUAL
ST is a registered trademark of AT&T.
Any other trademarks mentioned in this manual are acknowledged to be the property
of the trademark owners.
FCC/IC STATEMENTS AND TRADEMARKS

RS-232 TO FIBER OPTIC MULTIPLEXOR
Contents
Chapter Page
1. Specifications ............................................................................................. 1
2. Introduction ............................................................................................... 3
2.1 General ................................................................................................ 3
2.2 Physical Description ............................................................................ 4
3. Installation .................................................................................................. 6
3.1 Rackmounting ..................................................................................... 6
3.2 AC Power Connection ........................................................................ 8
3.3 Optical-Cable Connection .................................................................. 8
3.4 Channel-Cable Connection ................................................................ 9
4. Configuration and Operation ................................................................. 10
4.1 Modes of Operation .......................................................................... 10
4.2 Operating the Multiplexors ............................................................. 13
4.3 Interface Description ........................................................................ 13
5. Troubleshooting ...................................................................................... 18
5.1 General .............................................................................................. 18
5.2 Troubleshooting Procedure ............................................................. 18
5.3 Testing ............................................................................................... 19
5.4 No Data Transfer on All Channels .................................................. 23
5.5 Data Transfer Is Badly Corrupted .................................................... 25
5.6 Calling BLACK BOX ......................................................................... 26
5.7 Shipping and Packaging ................................................................... 26

1
CHAPTER 1: Specifications
Approvals — FCC Class A, IC Class/classe A
Multiplexing
Technique — Time-division
User Channels — MX035 units: (8); (24) in Triple Asynchronous Mode
with 3-to-1 adapter cable (EYN355)
MX036 units: (16); (48) in Triple Asynchronous Mode
with 3-to-1 adapter cable (EYN355)
Interface — Channel: Serial EIA RS-232C/CCITT V.24, DCE
Composite: Dual fiberoptic
Protocols — Asynchronous or synchronous (user-selectable)
Clock — Internal or external from local DTE (user-selectable)
Operating Mode — Full duplex over dual fiberoptic cable
Speeds — Channel: Asynchronous: Transparent to all speeds up
to 19,200 bps; Synchronous: 1200, 2400, 4800,
9600, or 19,200 bps (user-selectable)
Composite: 11 Mbps
Maximum
Distance — 7200 ft. (1.36 mi., 2.2 km) over cable with a 50-µm
fiber core
Wavelength — 830 ±15 nm
Optical Output — -22 dBm typical into 50-µm core
Receiver
Sensitivity — -33 dBm minimum at 10-9 bit error rate
Dynamic Range — 11 dBm for 50-µm core
Bit Error Rate — Better than 10-9 over the full receiver range
1. Specifications

2
RS-232 TO FIBER OPTIC MULTIPLEXOR
User Controls — Rear-mounted 6-position DIP switches:
MX035 units: (8); MX036 units: (16)
Indicators — (2) Front-panel LEDS: Power, SDCD (carrier detect)
Connectors — (10) or (18) Rear-mounted:
Channel: MX035 units: (8) DB25 female;
MX036 units: (16) DB25 female;
Composite: 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 (PGD), 2 (TXD), 3 (RXD), 5 (CTS), 6 (DSR),
7 (SGD), 8 (DCD), 14 (STXD), 15 (TXC), 17 (RXC or
SRXD), and 20 (DTR)
Power — MX035A, MX036A units: Directly from outlet:
Input range: 95 to 130 VAC, 50 to 60 Hz, 1 A;
MX035AE, MX036AE units: Directly from outlet:
Input range: 230 VAC, 50 to 60 Hz, 0.5 A
Fuse — MX035A, MX036A units: 1 A, 120-VAC Slo-Blo;
MX035AE, MX036AE units: 0.5 A, 220-VAC Slo-Blo
Temperature — 32 to 113˚ F (0 to 45˚ C) ambient
Humidity — 0 to 95%, noncondensing
Enclosure — Metal, with rubber feet
Size — 3.4"H x 16.6"W x 12.2"D (8.6 x 42.2 x 31 cm)
Weight — 8.4 lb. (3.8 kg)

3
CHAPTER 2: Introduction
2.1 General
The RS-232 to Fiber Optic Multiplexor is available in two major model types:
one with 8 channels (product codes beginning with “MX035”), and one with
16 channels (product codes beginning with “MX036”). Both models are built
from the same circuit board and are identical in every way except for the
number of channels. An 8-channel unit can communicate with channels 1
through 8 of the 16-channel unit if the two units are connected together.
There are two other points of difference in this product line. First, product
codes in which the letter “A” follows “MX035” or “MX036” use 120 VAC;
codes with the letters “AE” in this position use 240 VAC. Second, codes that
end with the “A” or “AE” have SMA 905 fiberoptic connectors; codes in which
“-ST” follows the “A” or “AE” have ST®connectors.
Using rear-panel switches, you can independently configure each full-
duplex RS-232 channel of either multiplexor in a pair of these muxes for one
of five modes of operation, three asynchronous and two synchronous. The
multiplexor is transparent to data rates up to 19,200 bps in the asynchronous
modes, and is transparent to sub-protocols and data formats in both the
asynchronous and synchronous modes.
1. The first mode of operation is single-channel asynchronous: The
multiplexor transmits one data signal, one DTR/CTS-handshaking control,
and no other signals.
2. The second mode is only slightly different: In addition to the DTR/
CTS handshaking, a second, auxiliary (control or data) signal is present.
3. The third mode is triple-channel asynchronous: The multiplexor sends
three separate data signals on each channel, across a 3-to-1 adapter cable (our
product code EYN355), without any handshaking or control signals. This
allows you to connect three asynchronous RS-232 “dumb terminals” to each of
the mux’s ports; in this mode, 8-channel units can handle 24 async data-only
channels and 16-channel units can handle 48 async data-only channels.
4. The fourth mode is synchronous with internal clocking (the multiplexor
supplies the clock to the terminal device). This mode supports transmission
of one handshaking signal, which allows the Data Terminal Ready (DTR)
input at one end of the system to control the Clear to Send (CTS) output at
the other end. Data rates of 1200, 2400, 4800, 9600, and 19,200 bps are
available.
2. Introduction

4
RS-232 TO FIBER OPTIC MULTIPLEXOR
5. The fifth mode is synchronous with external clocking (the terminal
device supplies the clock to the multiplexor). Like all other modes but the
third, this mode supports DTR/CTS handshaking. The mux will accept and
adapt to any externally-clocked data rate up to 14,400 bps. This is identical to
Mode 2, with the exception that the auxiliary signal is clock timing from the
DTE (terminal device).
The multiplexor is housed in a metal enclosure. The case has rubber feet
for stand-alone use on a table top or shelf, but can also be rack-mounted in
a standard 19-inch rack by attaching the optional rackmounting brackets
(product code RM901).
2.2 Physical Description
This section describes the physical characteristics of the multiplexor.
The front panel (see Figure 2-1, below) of the mux has no controls, but
has two LED indicators in the lower right-hand corner. The red LED at the
extreme right is the POWER ON indicator. The green LED to its left, labeled
“SDCD” (System Data Carrier Detect), indicates that an optical signal is being
received. It does not indicate that the signal is error-free or that the
multiplexor is in synchronization with the incoming signal. If the optical-
receiver connector (RX) is disconnected and open, it is possible that external
light sources could trigger the optical receiver and cause this LED to light.
The components on the rear panel of the multiplexor are shown in
Figure 2-2 on the next page, which illustrates a 16-channel unit. The rear
panel of the 8-channel mux is the same, except that a plate covers the holes
for the connectors and switches of channels 9 through 16.
1. Optical-Transmitter Connector: SMA or ST compatible connector for the
optical transmitter.
Figure 2-1. The front panel.
SDCD POWER

5
CHAPTER 2: Introduction
2. Optical-Receiver Connector: SMA or ST compatible connector for the
optical receiver.
3. Switch-Setting Chart: Identifies the channel-configuration-switch settings.
4. Channel-Configuration Switches: A 6-position DIP switch for each
channel, which you can use to select the internal transmit clock/data rate,
or secondary transmit data in place of the transmit clock. (See Section
4.1.)
5. Channel-I/O Connector: A DB25 female connector for each channel.
The 16-channel unit has 16 connectors and switches; the 8-channel unit
has 8 connectors and switches with a cover plate over the unused slots.
6. Locking-Screw Sockets (2 per connector): 4-40 threaded female standoffs
to accept locking screws on the cable connector.
7. Fuse Holder: Holds a Slo-Blo AC-line fuse (1 A for 120-VAC units,
0.5 A for 240-VAC units).
8. AC-Power Cord: Has a U.S. standard 3-prong plug for 120-VAC units
or a standard plug for the country in which the unit is sold for 240-VAC
units. AC-line voltage is printed directly above the point at which the
power cord enters the rear panel.
Figure 2-2. The rear panel.
F
U
S
E
TX RX
3 4 5 6 7
81 2

6
RS-232 TO FIBER OPTIC MULTIPLEXOR
This section describes the installation procedures for the multiplexor in a
standard 19-inch rack and explains how to connect the optical cable and
the terminal devices.
If possible, test the pair of multiplexors and the optical cable with each
other before installation. Testing before installation will reveal any damage
that might have occurred to either mux or cable during shipping, so you’ll
know that the items weren’t damaged during installation. This initial testing
and troubleshooting are much easier when both muxes are placed close to
each other and both ends of the cable are easily accessible.
Standard units of this multiplexor are supplied with four rubber feet for
placement on a table top or shelf. If it is necessary to remove the feet for
another type of mounting, first remove only one foot and check the type of
mounting screw used.
If a 4-40 machine screw is used to mount the feet, the unit is an early one
that uses the foot-mounting screws to hold the internal printed circuit board in
place. DO NOT REMOVE ALL THE SCREWS AT THE SAME TIME. Remove
only one foot at a time and replace its mounting screw with a 4-40 x 3/16-inch
flathead screw. (Holes in the chassis bottom are countersunk.)
If the foot-mounting screws are self-tapping sheet-metal screws, the unit
is a newer one with separate mounting holes for the feet. The feet can be
removed without replacing the screws.
3.1 Rackmounting
For rackmounting, a pair of brackets are available for the necessary mounting
flanges (product code RM901). To attach the rackmount brackets, first
remove the four screws closest to the front of the chassis from one side of
the multiplexor chassis. See Figure 3-1 on the next page.
Do not remove the screws from both sides at the same time, because the
front panel may fall out. If this happens, the front panel can be replaced by
inserting it back into the multiplexor chassis and pressing against the top and
bottom of the front panel at the same time, holding it against the edge of the
internal printed circuit board, while positioning the panel to line up its
threaded inserts with the holes in the multiplexor chassis.
3. Installation

7
CHAPTER 3: Installation
After removing the screws, place one of the rackmount brackets against the
side of the multiplexor, lining up the four round holes in the long side of the
bracket with the holes from which the screws were just removed. Then use the
same screws that were previously removed to attach the rackmount bracket.
The holes in the brackets are spaced 1.75 inches (4.45 cm) apart, located
at equal distances from the top and bottom of the multiplexor.
The multiplexor is 3.4 inches (8.7 cm) high and requires 3.5 inches
(8.9 cm) of vertical rack space. Additional vertical space above and below the
multiplexor may be required to provide clearance for cooling air flow in and
out of the chassis.
For air cooling, the multiplexor must be mounted to allow unobstructed air
flow into and out of the perforations in the sides and top of the mux chassis.
If the mux is mounted in a rack cabinet, minimum air flow of 120 cubic feet
(3.4 cubic meters) per minute through the cabinet must be provided. If other
equipment is mounted above the mux in the same rack, it must not block air
flow through the perforations in the top of the mux chassis. Also, the sides of
the rack cabinet must be far enough from the sides of the mux chassis to
allow air flow into the perforations on the sides of the mux chassis. (Virtually
all rackmount cabinets have adequate clearance in this area, but this should
be checked.) If mounting another piece of equipment directly above the mux
blocks air flow out of the perforations on the top of the mux, a spacer panel
should be placed between the two units to provide clearance.
Figure 3-1. Attaching a rackmount bracket.
MULTIPLEXOR FRONT PANEL

8
RS-232 TO FIBER OPTIC MULTIPLEXOR
3.2 AC Power Connection
The 120-VAC version of the multiplexor requires 95 to 130 VAC, 50 to 60 Hz
power, at a maximum current of 1 ampere. It is equipped with a U.S.-standard
three-prong power plug that should be connected to a properly grounded AC
outlet. Do not operate the mux with the chassis ungrounded.
Units of 240-VAC versions require 50 to 60 Hz power at a maximum current
of 0.5 amp. The power cord is provided with a plug that matches the standard
for the country for which the unit is sold.
3.3 Optical-Cable Connection
The multiplexor operates in full-duplex mode, requiring a two-fiber cable
or two fibers of a multifiber cable.
Multifiber cables usually have number labels on each connector with both
ends of the same fiber having the same number. This type of cable should
have the same-numbered fiber connected to the transmitter of the first mux
at one end of the cable and the receiver of the second mux at the other end
of the cable.
Before connecting optical cables to the mux’s optical transmitter and
receiver, verify that both the cable terminations and the optical transmitter
and receiver receptacles are clean. It is good practice to cover the connectors
with the provided plastic caps when the connectors are not in use.
To connect fiberoptic cables to your mux, insert each cable’s male
connector into the matching female connector of the optical transmitter or
receiver, as shown in Figure 3-2 on the next page. If the connectors are SMA
type, finger-tighten the coupling nut. If the connectors are ST type, gently
twist the male connector to lock it into place.
For SMA connectors, failure to tighten the coupling nut can cause
inadequate optical coupling between the cable and the mux, especially
at the transmitter.
CAUTION!
Do not use any tools to tighten the connectors under any circumstances.
Excessive tightening of a connector can result in damage to the
connector and possibly to the optical transmitter or receiver as well.

9
CHAPTER 3: Installation
Take care in the placement of the optical cables to ensure that the cables are
not subjected to stress at or near the optical connectors. Take special caution
to ensure that there are no sharp bends in the cable near the connectors. We
recommend that some form of strain relief be provided to ensure that no
stress is placed on the cable connectors by either tension on the cable or
movement of the multiplexor chassis.
3.4 Channel-Cable Connection
The channel connectors of the multiplexor are RS-232 standard DB25
females, requiring a matching male connector on the interface cable.
A 4-40 female threaded standoff is located at each end of the connector to
accept locking screws from the male cable connector. Unless the connection
to an individual channel is expected to be temporary, we recommend that
connectors with locking screws be used and that these screws be secured in
the threaded standoffs provided, to ensure that the cables will not be
accidentally pulled out of the connectors.
If a three-channel adapter cable (product code EYN355) is being connected
to a channel of the mux, the male connector of the adapter cable should be
secured to the mux’s channel connector using the provided locking screws.
The RS-232 cables connecting to the adapter should be secured to the female
connectors of the adapter cable in the same way.
Figure 3-2. Connecting fiberoptic cables.
TX RX
TX
RX
FIBER OPTIC CABLE
MULTIPLEXOR
OPTICAL

10
RS-232 TO FIBER OPTIC MULTIPLEXOR
This chapter describes how to configure each channel for the desired mode
of operation and how to operate the multiplexor.
4.1 Modes of Operation
On each channel of the multiplexor, one of five modes of operation
can be independently selected:
1. Single asynchronous data line with one control signal.
2. Single asynchronous data line with one control and one auxilary signal.
3. Three async data lines on the same port without control signals
(using 3-to-1 adapter cable).
4. Single synchronous data line using internal clock.
5. Single synchronous data line using external clock.
See Section 4.3 for more detailed information on the supported control
signals and their functions.
Select the operating mode of each channel with the DIP switch located
directly above that channel’s connector. The function of each position in the
switch is indicated by the chart in the upper left-hand corner of the rear panel
(see Figure 4-1 on the next page).
4.1.1 S INGLE A SYNCHRONOUS D ATA L INE W ITH O NE C ONTROL S IGNAL (M ODE 1)
In this mode of operation, the asynchronous Transmit Data signal fed into
one multiplexor is transmitted to the Receive Data output of the other
multiplexor, the Data Terminal Ready input (Pin 20) at one end controls the
Clear to Send signal (Pin 5) at the other end, and no other signals are passed.
This minimal communication will suffice for many types of “dumb terminals.”
The mux is transparent to asynchronous data rates on a channel in this mode
up to 19,200 bps. To set a given channel for this mode, set all of that
channel’s DIP-switch positions to OFF.
4. Configuration and Operation

11
CHAPTER 4: Configuration and Operation
4.1.2 S INGLE A SYNCHRONOUS D ATA L INE W ITH C ONTROL AND A UXILIARY S IGNALS
(M ODE 2)
There is only one difference between this mode and Mode 1: A second signal
can be fed into RS-232 Pin 14 (Secondary Transmit Data) and passed to Pin
17 of the other multiplexor. This “auxiliary” signal can be a data or control
signal. To set a given channel for this mode, set that channel’s “STD” switch
position (position 6, the one at the extreme right-hand end of the switch
block) to ON and set all other switch positions for that channel OFF. (If any
other switch positions are left ON, other channels might malfunction.)
NOTE
The auxiliary signal fed into the mux on Pin 14 will be “reflected” back
out Pin 15 of the same connector. See Section 4.1.5 for the reason why.
4.1.3 T RIPLE A SYNCHRONOUS D ATA L INES W ITHOUT C ONTROLS (M ODE 3)
In this mode, data is carried on not only the normal data line but across the
DTR/CTS control line and the auxiliary line as well, allowing you to attach
three standard RS-232 devices to one multiplexor channel with a 3-to-1
adapter cable (our product code EYN355). This cable has one male
connector that plugs into the mux channel’s input connector and three
female connectors labeled A (2-3), B (14-17), and C (20-5). The only signals
supported by this cable are Transmit Data, Receive Data, Protective Ground,
and Signal Ground.
Figure 4-1. DIP-Switch settings.
F
U
S
E
TX RX
ON
OFF
19.2K 4.8K 1.2K
9.6K 2.4K STD
DIP SWITCH
All positions OFF: Asynchronous, one control signal (Mode 1).
“STD”: (a) Asynchronous, control and auxiliary signals (Mode 2);
(b) triple asynchronous, no control signals (Mode 3); or
(c) synchronous, external clock received on Pin 14 (Mode 5).
“19.2K,” “9.6K,” “4.8K,” “2.4K,” “1.2K”: Data rate, in bits per
second, regulated with synchronous internal clock (Mode 4).

12
RS-232 TO FIBER OPTIC MULTIPLEXOR
Signals fed into the A connector at one end of the system (attached to a
terminal device connected to one mux) will be received at the A connector at
the other end of the system (attached to a terminal device connected to the
other mux), and vice versa. The B and C connectors work the same way. The
numbers on each connector are the pin numbers on the mux channel’s
connector through which the signals actually pass. For more detailed
information, see Section 4.3.3.
To set a given channel for this mode, set that channel’s STD switch position
ON, all others OFF.
NOTE
Data coming into the mux from the B device on Pin 14 will be present on
Pin 15 of the mux’s input connector. See Section 4.1.5 for the reason why.
4.1.4 S YNCHRONOUS D ATA L INE WITH I NTERNAL C LOCK (M ODE 4)
For a channel in this mode of operation, the local multiplexor supplies the
transmit clock to its attached terminal device on Pin 15 and transmits the
same clock, with the terminal device’s synchronous transmit data, to the
remote multiplexor. The remote mux (which can be set for either internal
or external clocking) will output the clock signal from the local mux on
Pin 17 of the corresponding channel’s connector.
Data Terminal Ready controls Clear to Send the same way it does in Modes
1 and 2. Available internal-clock data rates are 1200, 2400, 4800, 9600, and
19,200 bps.
To set a given channel for this mode, set the position of that channel’s DIP
switch that corresponds to the desired data rate (see Figure 4-1 on the next
page) ON, and all other positions OFF. A channel will not operate properly
with two data rates selected, and any other channel that has either of those
data rates selected will also malfunction.
4.1.5 S YNCHRONOUS D ATA L INE WITH E XTERNAL C LOCK (M ODE 5)
For a channel in this mode, the local multiplexor receives the transmit clock
from its attached terminal device on Pin 14 and passes it on to the remote
multiplexor. The remote mux (which can be set for either internal or
external clocking) will output the clock signal from the local mux on Pin 17
of the corresponding channel’s connector. (This mode is essentially the same
as Mode 2: clocking is carried by the auxiliary signal instead of data or
another type of control.)

13
CHAPTER 4: Configuration and Operation
The mux can accept and adapt to any data rate up to 14,400 bps on a
channel in this mode. To set a given channel for this mode, set that channel’s
STD switch position ON, all others OFF.
NOTE
Any time the mux’s STD switch position is ON (Mode 2, 3, or 5), the
signal input to the mux on Pin 14 will be retransmitted back out Pin 15.
This feature is not particularly useful for Mode 2 or 3, but for Mode 5 it
allows the mux to get the external clock on Pin 14 (Secondary Transmit
Data) and echo it on Pin 15 (Transmit Clock). This feature will also come
in handy if you ever need to do end-to-end testing (see Section 5.3.1).
4.2 Operating the Multiplexors
After connecting the multiplexors with the optical cable, connecting the
terminal devices to the individual channels (either directly or through the
adapter cables), and setting the channel configuration switches, connect both
multiplexors to their AC power sources. Note that the muxes have no AC
power switch. Each multiplexor is turned ON and OFF by plugging and
unplugging its power cord. Verify that the red POWER LED of each
multiplexor comes on when AC power is connected, and that the green
SDCD LEDs of both multiplexors come on when power is applied to the
second multiplexor.
Try transmitting through the multiplexors. If data does not seem to be
passing through, or if there seem to be errors in the data being transmitted,
see Chapter 5.
4.3 Interface Desription
This section describes the basic operating principles of the multiplexor and
the functions and characteristics of the channels’ electrical interface signals.
Instructions are also given on how to connect three asynchronous terminal
devices to a single channel of the multiplexor.
4.3.1 M ETHOD OF M ULTIPLEXING AND D EMULTIPLEXING
Each channel of the multiplexor transmits three signals in each direction. All
signals in all channels are sampled simultaneously at a rate of 76.8 KHz. The
samples are then transmitted serially on the fiberoptic link and reconstructed
at the receiving end, where they are all simultaneously transferred in parallel
to the interface outputs.

14
RS-232 TO FIBER OPTIC MULTIPLEXOR
This sampling and reconstruction induces variable propagation delays on
each signal, since signals coming into the mux from external sources will not
necessarily be synchronized to the internal sampling clock.
Maximum timing distortion is 13.2 µs, which is 1/4 of one bit time at the
maximum input data rate of 19.2 Kbps.
Total propagation delay of signals from the input of one multiplexor to the
corresponding output of the other multiplexor is 14 to 27 µs, plus 5 ns per
meter of fiberoptic cable. All of these time delays are the same for both the
8-channel unit and the 16-channel unit.
4.3.2 S IGNAL F UNCTIONS
Functions of the multiplexor channel interface signals are described below.
All outputs except Data Set Ready and Data Carrier Detect go to the negative
(MARK or OFF) state if the optical signal is not being received from the other
multiplexor. Also, all inputs will appear to be a negative level if they are left
open.
Table 4-1 on page 16 shows all of the signals, their pins, directions, and
originating and receiving devices.
Data Set Ready (DSR, Pin 6)
All DSR outputs of all channels are connected in parallel to a common pull-
up resistor, and will be at the true level whenever the multiplexor is powered
ON.
Data Carrier Detect (DCD, Pin 8)
All DCD outputs of all channels are connected in parallel to a separate pull-
up resistor in the same fashion as the Data Set Ready output, and will also
always be true whenever the multiplexor is powered ON.
Transmit Data (TXD, Pin 2) and Receive Data (RXD, Pin 3)
The signal fed into the Transmit Data input (Pin 2) of the channel is
transmitted through the optical link and appears at the other multiplexor
channel as the Received Data output (Pin 3).

15
CHAPTER 4: Configuration and Operation
Data Terminal Ready (DTR, Pin 20) and Clear to Send (CTS, Pin 5)
The signal fed into the Data Terminal Ready input (Pin 20) of a multiplexor
channel is transmitted to the other multiplexor, where it appears at the Clear
to Send output (Pin 5). The Clear to Send output is true whenever Data
Terminal Ready is true at the other multiplexor, even if Request To Send
(RTS, Pin 4) is false. (The multiplexor has no Request To Send input.) It is
possible that some terminal devices connected to the multiplexor may be
confused by this condition and not work properly.
Transmit Clock (TXC, Pin 15), Receive Clock (RXC, Pin 17), and Secondary
Transmit Data (STXD, Pin 14)
The received signal that appears as an output at Pin 17 (Receive Clock) of
one of the local multiplexor’s channels has two possible sources at the remote
mux:
If the corresponding channel of the remote multiplexor is configured for
internal-clock synchronous operation (Mode 4), that multiplexor’s Transmit
Clock output (Pin 15) also appears at the Receive Clock (Pin 17) output of
the local mux.
If the corresponding channel of the remote multiplexor has its channel-
configuration switch set with STD ON and all other positions OFF (Mode 2, 3,
or 5), any signal fed into the remote multiplexor on that channel on
Pin 14 (Secondary Transmit Data) appears on that channel at Pin 15
(Transmit Clock) and is transmitted to the local multiplexor, where it
appears at the Receive Clock (Pin 17) output.

16
RS-232 TO FIBER OPTIC MULTIPLEXOR
Each signal’s originating device(s) are shown by the letter “O.” Each signal’s
destination device(s) are shown by the letter “D.” Positive voltage is shown by
“+V.” Signal directions are shown by arrows.
Channel is in Mode 1 (Async, 1 Control):
Signal Local Local- Local Remote Remote- Remote Signal
Device Mux Pin Mux Mux Mux Pin Device
TXD O 2 3 D RXD
RXD D 3 2 O TXD
CTS D 5 20 O DTR
DSR D 6 (+V) O O (+V) 6 D DSR
Sig. Gnd. 7 7 Sig. Gnd.
DCD D 8 (+V) O O (+V) 8 D DCD
DTR O 20 5 D CTS
Channel is in Mode 4 (Internal Sync):
All of the signals shown above, plus these:
TXC D 15 O 17 D RXC
RXC D 17 O 15 D TXC
Channel is in Mode 2 (Async, 2 Controls), 3 (Triple Async), or 5 (Ext. Sync):
All of the signals shown for Mode 1, plus these:
STXD O 14 17 D RXC
TXC D 15 15 D TXC
RXC D 17 14 O STXD
Table 4-1. Signal Paths (Per Channel)

17
CHAPTER 4: Operation
4.3.3 C ONNECTING T HREE A SYNCHRONOUS L INES TO O NE M ULTIPLEXOR C HANNEL
As described in Section 4.1.3, three separate asynchronous data-only channels
(no control signals) can be transmitted through one channel of the
multiplexor. To connect three standard RS-232 cables to one multiplexor
channel requires an adapter cable (product code EYN355). This cable has
female connectors labeled A, B, and C, and is wired according to Table 4-2
below.
If any of the three terminal devices on a given channel require the Data Set
Ready, Clear to Send, or Data Carrier Detect signals, these can be provided in
the following ways:
• Data Set Ready: Pin 6 of the 3-to-1 adapter cable’s female connector(s)
must be wired to Pin 6 of the cable’s male connector.
• Data Carrier Detect: Pin 8 of the adapter cable’s female connector(s)
must be wired to Pin 8 of the cable’s male connector.
(Neither of the above arrangements is standard with the normal adapter cable
EYN355, but we will be happy to customize the cable for you. Call us for a
quote.)
• Clear to Send: On the adapter cable, jumper together Pins 4 and 5
of the female connector corresponding to the desired device.
Table 4-2. Adapter-Cable Pinning
Male Connector Female Connector(s)
Pin Number: Pin Number(s):
1 ---------------------------------------------------------------- A-1, B-1, C-1
2 ---------------------------------------------------------------- A-2
3 ---------------------------------------------------------------- A-3
5 ---------------------------------------------------------------- C-3
7 ---------------------------------------------------------------- A-7, B-7, C-7
14 -------------------------------------------------------------- B-2
17 -------------------------------------------------------------- B-3
20 -------------------------------------------------------------- C-2