Black Box ME935A User manual

CUSTOMER
SUPPORT
INFORMATION
Order toll-free in the U.S.: Call 877-877-BBOX (outside U.S. call 724-746-5500)
FREE technical support 24 hours a day, 7 days a week: Call 724-746-5500 or fax [phone]
Mailing address: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018
Web site: www.blackbox.com • E-mail: [email protected]
NOVEMBER 2000
ME935A
Async Short-Haul Modem MP
Power TD RD
Control
IN
Control
OUT Loopback
Test

1
TRADEMARKS
Trademarks
AT&T is a registered trademark of American Telephone and Telegraph Company.
Any other trademarks mentioned in this manual are acknowledged to be the
property of the trademark owners.

2
ASYNC SHORT-HAUL MODEM MP
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 la classe A prescrites dans le Règlement sur le
brouillage radioélectrique publié par le ministère des Communications du Canada.

3
NOM STATEMENT
NORMAS OFICIALES MEXICANAS (NOM)
ELECTRICAL SAFETY STATEMENT
INSTRUCCIONES DE SEGURIDAD
1. Todas las instrucciones de seguridad y operación deberán ser leídas antes de
que el aparato eléctrico sea operado.
2. Las instrucciones de seguridad y operación deberán ser guardadas para
referencia futura.
3. Todas las advertencias en el aparato eléctrico y en sus instrucciones de
operación deben ser respetadas.
4. Todas las instrucciones de operación y uso deben ser seguidas.
5. El aparato eléctrico no deberá ser usado cerca del agua—por ejemplo, cerca
de la tina de baño, lavabo, sótano mojado o cerca de una alberca, etc..
6. El aparato eléctrico debe ser usado únicamente con carritos o pedestales que
sean recomendados por el fabricante.
7. El aparato eléctrico debe ser montado a la pared o al techo sólo como sea
recomendado por el fabricante.
8. Servicio—El usuario no debe intentar dar servicio al equipo eléctrico más allá
a lo descrito en las instrucciones de operación. Todo otro servicio deberá ser
referido a personal de servicio calificado.
9. El aparato eléctrico debe ser situado de tal manera que su posición no
interfiera su uso. La colocación del aparato eléctrico sobre una cama, sofá,
alfombra o superficie similar puede bloquea la ventilación, no se debe colocar
en libreros o gabinetes que impidan el flujo de aire por los orificios de
ventilación.
10. El equipo eléctrico deber ser situado fuera del alcance de fuentes de calor
como radiadores, registros de calor, estufas u otros aparatos (incluyendo
amplificadores) que producen calor.
11. El aparato eléctrico deberá ser connectado a una fuente de poder sólo del
tipo descrito en el instructivo de operación, o como se indique en el aparato.

4
ASYNC SHORT-HAUL MODEM MP
12. Precaución debe ser tomada de tal manera que la tierra fisica y la polarización
del equipo no sea eliminada.
13. Los cables de la fuente de poder deben ser guiados de tal manera que no
sean pisados ni pellizcados por objetos colocados sobre o contra ellos,
poniendo particular atención a los contactos y receptáculos donde salen del
aparato.
14. El equipo eléctrico debe ser limpiado únicamente de acuerdo a las
recomendaciones del fabricante.
15. En caso de existir, una antena externa deberá ser localizada lejos de las lineas
de energia.
16. El cable de corriente deberá ser desconectado del cuando el equipo no sea
usado por un largo periodo de tiempo.
17. Cuidado debe ser tomado de tal manera que objectos liquidos no sean
derramados sobre la cubierta u orificios de ventilación.
18. Servicio por personal calificado deberá ser provisto cuando:
A: El cable de poder o el contacto ha sido dañado; u
B: Objectos han caído o líquido ha sido derramado dentro del aparato; o
C: El aparato ha sido expuesto a la lluvia; o
D: El aparato parece no operar normalmente o muestra un cambio en su
desempeño; o
E: El aparato ha sido tirado o su cubierta ha sido dañada.

5
CONTENTS
Contents
Chapter Page
1. Specifications............................................................................................................6
2. Introduction ............................................................................................................7
2.1 Overview ..........................................................................................................7
2.2 Features ..........................................................................................................7
3. Configuration ..........................................................................................................8
3.1 Quick Set-Up Instructions..............................................................................8
3.1.1 Point-To-Point Configuration ..............................................................8
3.1.2 Multipoint Configuration ....................................................................8
3.2 DCE/DTE Switch Settings ............................................................................9
3.3 Special Configuration ....................................................................................9
4. Installation..............................................................................................................11
4.1 Twisted-Pair Wiring Overview......................................................................11
4.1.1 Twisted-Pair Connection Using Terminal Blocks ............................12
4.1.2 Twisted-Pair Connection Using RJ-11 ................................................12
4.2 Wiring For Multipoint Circuits....................................................................13
4.2.1 Daisychain Topology ..........................................................................13
4.2.2 Star Topology ......................................................................................14
4.3 RS-232 Connection ......................................................................................14
5. Operation ..............................................................................................................15
5.1 LED Indicators..............................................................................................15
5.2 Loopback Test Modes ..................................................................................15
5.2.1 Local Analog Loop ..............................................................................15
5.2.2 Remote Analog Loop ..........................................................................16
6. Troubleshooting ....................................................................................................17
Appendix A. Cable Recommendations ....................................................................19
Appendix B. Interface Pin Assignments....................................................................20
Appendix C. Block Diagram ......................................................................................21

6
ASYNC SHORT-HAUL MODEM MP
1. Specifications
Transmission Format— Asynchronous
Transmission Line— 19 to 26 AWG twisted pair
Range— See table in Appendix A
Serial Interface— EIA RS-232 (CCITT V.24), DB25 female
Twisted-Pair Interface— Terminal blocks, RJ-11 jack
Data Rates— Up to 115,200 bps
Applications— Point-to-point, multipoint
Indicators— Tri-state for transmit data, receive data, control in,
control out; dual-state for power, loopback test
Diagnostics— Local Analog Loopback (LAL), Remote Analog
Loopback (RAL)
Optical Isolation— 2500V RMS minimum
Surge Suppression— Over-voltage protection for opto-isolators via Silicon
Avalanche Diodes
Temperature Range— 32 to 140°F (0 to 60°C)
Humidity Tolerance— 5 to 95%, noncondensing
Maximum Altitude Range— Up to 15,000 feet (4572 m)
Power Supply— Wallmount, outputs 10 VAC, 700 ma
Size— 1.5"H x 4.1"W x 5"D (3.8 x 10.4 x 12.7 cm)
Weight— 13.2 oz. (374.2 g) without transformer

7
CHAPTER 2: Introduction
2. Introduction
2.1 Overview
The Async Short-Haul Modem MP is equipped with a virtual wish list of “bells and
whistles.” Point-to-point or multipoint applications are supported. Two separate
control signals may be passed (one each way), each with switch-selectable pin
assignments. Data lines are protected from ground loops and electrically volatile
environments by optical isolation and Silicon Avalanche Diodes. System integrity
can be evaluated using two built-in test modes: local analog loopback and remote
analog loopback. Tri-state LEDs monitor transmit data, receive data, and control
signals. Finally, 4-wire connections may be made using either RJ-11 jack or terminal
blocks—both are included.
In addition, the Async Short-Haul Modem MP is perfect for low-power RS-232
environments. The Modem is AC powered, and therefore is the recommended
solution for RS-232 environments whose interface voltages are below RS-232
specifications. The Modem supports data rates to 115.2 kbps and extends RS-232
transmission distances up to 14 miles (22.5 km) over two twisted pairs.
The Modem is housed in a sturdy metal case and comes with either 115 or 220V
external transformers.
2.2 Features
• Data rates to 115.2 kbps.
• Built-in optical isolation and high-speed surge protection.
• Distances up to 14 miles (19 AWG TWP @ 1200 bps).
• Tri-state LED indicators.
• Point-to-point or multipoint applications.
• Local and remote loopback test modes.
• DCE/DTE switch-selectable.
• Hardware and software flow control support.
• Externally powered.

8
ASYNC SHORT-HAUL MODEM MP
3. Configuration
The Async Short-Haul Modem MP features externally accessible configuration
switches (two DCE/DTE switches and a DIP-switch set), located on the underside
of the unit; there is no need to open the case to configure the Modem.
3.1 Quick Set-Up Instructions
In the majority of applications, you won’t need an in-depth knowledge of the
Modem’s capabilities to get up and running. The following quick-setup DIP-switch
configurations cover most Modem operating environments. (Note that DIP-switch
8 is not used.)
3.1.1 P OINT -T O -P OINT C ONFIGURATION
If you are installing these Modems in a point-to-point application with a computer,
printer, or terminal, configure the DIP switches on both Modems as follows:
Switch Number 1 2 3 4 5 6 7
Positions OFF OFF OFF ON ON ON OFF
3.1.2 M ULTIPOINT C ONFIGURATION
The Modem supports multipoint operation in either daisychain or star
configurations.
In a multipoint topology, you must configure the master Async Short-Haul Modem
MP’s DIP switches differently than those of the slave Modems. These are the
proper DIP-switch settings for a daisychain topology:
Switch Number 1 2 3 4 5 6 7
Master Positions ON ON ON OFF OFF OFF OFF
Slave Positions ON ON ON OFF OFF OFF ON

9
CHAPTER 3: Configuration
3.2 DCE/DTE Switch Settings
Correct setting of the DCE/DTE switches eliminates the need for RS-232 crossover
cables. If the RS-232 device you are connecting to the Modem is a PC, terminal, or
host (or is wired like one), set both of the DCE/DTE switches to DCE. If the RS-
232 device you are connecting to the Async Short-Haul Modem MP is a modem or
multiplexor, or is wired like one, set both of the DCE/DTE switches to DTE.
3.3 Special Configuration
If your Modem requires special configuration, use Table 3-1 as a guide. This table
shows all of the possible Modem switch settings. Following the table are brief
descriptions of the Control Input, Control Output, +Voltage Output and Carrier
Controlled by (Cin) parameters shown in the table.
Table 3-1. All possible switch settings for the Modem
Control Control +Voltage Carrier Switch Settings
Mode Input Output Output Controlled
(DCE/DTE) (CIn)(C
Out)(V Out) by (CIn)1234567
DCE 4 8 6 Disabled ON ON ON OFF OFF OFF OFF
DCE 4 8 6 Enabled ON ON ON OFF OFF OFF ON
DCE 4,11,20* 8 6 Disabled OFF ON ON ON OFF OFF OFF
DCE 4,11,20* 8 6 Enabled OFF ON ON ON OFF OFF ON
DCE 4 6 8 Disabled ON OFF OFF OFF ON ON OFF
DCE 4 6 8 Enabled ON OFF OFF OFF ON ON ON
DCE 4,11,20* 6 8 Disabled OFF OFF OFF ON ON ON OFF
DCE 4,11,20* 6 8 Enabled OFF OFF OFF ON ON ON ON
DTE 8 4 11,20** Disabled ON ON ON OFF OFF OFF OFF
DTE 8 4 11,20** Enabled ON ON ON OFF OFF OFF ON
DTE 5,6,8* 4 11,20** Disabled OFF ON ON ON OFF OFF OFF
DTE 5,6,8* 4 11,20** Enabled OFF ON ON ON OFF OFF ON
DTE 8 11,20** 4 Disabled ON OFF OFF OFF ON ON OFF
DTE 8 11,20** 4 Enabled ON OFF OFF OFF ON ON ON
DTE 5,6,8* 11,20** 4 Disabled OFF OFF OFF ON ON ON OFF
DTE 5,6,8* 11,20** 4 Enabled OFF OFF OFF ON ON ON ON
*Multiple input pins are "or-tied"—if any input goes low, carrier is dropped.
**Multiple output pins generate the same signal simultaneously.

10
ASYNC SHORT-HAUL MODEM MP
Control Input (Cin):
The Control Input signal is used by the local Async Short-Haul Modem MP as an
input signal to activate its transmitter (Enabled settings) and allow data
transmission to the remote device. This is required for half-duplex/switched-
carrier environments as well as in hardware flow-control applications. In the
Disabled settings, the Modem is always “turned on” and sends a continuous carrier
to the remote Modem.
Control Output (Cout):
The Control Output signal is transmitted by the local Modem to its attached DTE
device. This signal should be the same logic state as the Control Input signal on
the remote Modem. This signal is required in half-duplex/switched-carrier
environments or in hardware flow-control applications.
+Voltage Output (+Vout):
The +Voltage Output signal is a constant positive voltage that is sent from the
Modem to its attached DTE device.
Carrier Controlled by (Cin):
When Carrier Controlled by Control Input is Enabled, the Modem’s transmitter is
activated by the corresponding Cin Signal from the DTE. In effect, the Control
Input signal on the local Modem controls the presence of carrier and the Control
Output signal on the remote Modem. This setting is required in half-
duplex/switched-carrier environments or in hardware-flow-control applications.
When Carrier Control by Control Input is Disabled, the Modem sends a
continuous carrier and is always “turned on.”

11
CHAPTER 4: Installation
4. Installation
The Async Short-Haul Modem MP is easy to install. After configuring the DIP
switches and DCE/DTE switches, connect the two twisted pairs using either
terminal blocks or the RJ-11 jack. Figure 4-1 shows the location of the terminal
blocks and RJ-11 jack, as well as the female DB25 connector.
Figure 4-1. Rear view of Modem showing interface connectors.
4.1 Twisted-Pair Wiring Overview
These short-range modems are designed to work in pairs. You will need one at
each end of a 4-wire twisted-pair circuit. The pairs must be "dry" (unconditioned)
metallic wire, 19 to 26 AWG. The smaller gauges limit distance somewhat
compared with larger gauges. When you have completed wiring for your data
circuit, the pin connections should be as shown below:
XMT + ------------------------------------------- RCV +
XMT - ------------------------------------------- RCV -
G ----------To Shield (optional) G
RCV - ------------------------------------------- XMT -
RCV + ------------------------------------------- XMT +
RX+RX- GND TX+TX+
RS-232 Interface LinePower
}One Pair
One Pair
}

12
ASYNC SHORT-HAUL MODEM MP
4.1.1 T WISTED -P AIR C ONNECTION U SING T ERMINAL B LOCKS
If your two-twisted-pair line terminates in bare wires, strip the ends and connect
the individual leads to each Modem’s terminal block. Be sure the end-to-end
connections follow the diagram on page 11.
4.1.2 T WISTED -P AIR C ONNECTION U SING RJ-11
If your two-pair cable is terminated in an RJ-11 plug, you may use the RJ-11 jack in
the back of the Modem to make the connection. The RJ-11 jack on the Modem is
prewired for a standard telco wiring environment. To be sure you have the right
wiring, use the pinout below as a guide.
RJ-11 SIGNAL
1 ....................GND†
2 ....................RCV-
3 ....................XMT+
4 ....................XMT-
5 ....................RCV+
6 ....................GND†
For proper signal crossing between two Modems using RJ-11 connectors, wire the
twisted-pair cable according to the pinout below.
SIGNAL PIN# PIN# SIGNAL
GND†1 6 ..................GND†
RCV- 2 4 ..................XMT-
XMT+ 3 5 ..................RCV+
XMT- 4 2 ..................RCV-
RCV+ 5 3 ..................XMT+
GND†6 1 ..................GND†
†Connection to ground is optional
AT&T®standard modular color codes.
(These are standard color codes—yours may be different.)
1 - Blue
2 - Yellow
3 - Green
4 - Red
5 - Black
6 - White

13
CHAPTER 4: Installation
4.2 Wiring For Multipoint Circuits
The Modem supports multipoint applications using either a star or daisychain
topology. Both topologies require special wiring, as well as specific DIP-switch
settings for master and slave units.
4.2.1 D AISYCHAIN T OPOLOGY
Using a daisychain topology, you may connect as many as 10 Async Short-Haul
Modem MPs together in a master/slave arrangement. Maximum distance between
the units will vary based upon the number of drops, data rate, wire gauge, etc. Call
Technical Support for specific distance estimates.
Figure 4-2 shows how to wire the two-pair cables properly for an Async Short-Haul
Modem MP daisychain topology. Note that the ground connection is not needed.
Figure 4-2. Daisychain wiring.
HOST FIRST SLAVE OTHER SLAVE(S)
XMT+.........................RCV+ ...........................RCV+
XMT-..........................RCV- ............................RCV-
RCV+.........................XMT+ ...........................XMT+
RCV-..........................XMT- ............................XMT-
In a multipoint topology, you must configure the master Async Short-Haul Modem
MP’s DIP switches differently than those of the slave Modems. These are the
proper DIP-switch settings for a daisychain topology:
Switch Number 1 2 3 4 5 6 7
Master Positions ON ON ON OFF OFF OFF OFF
Slave Positions ON ON ON OFF OFF OFF ON

14
ASYNC SHORT-HAUL MODEM MP
4.2.2 S TAR T OPOLOGY
Using a star topology, you may connect several Modems together in a master/slave
arrangement. Maximum distance between the units will vary based upon the
number of drops, data rate, wire gauge, etc. Call Technical Support for specific
distance estimates.
Figure 4-3 shows how to wire the two-pair cables properly for a Modem star
topology. Note that the ground connection is not needed.
Figure 4-3. Modem star wiring.
HOST FIRST SLAVE SECOND SLAVE
XMT+ RCV+
RCV+
XMT- RCV-
RCV-
RCV+ XMT+
XMT+
RCV- XMT-
XMT-
In a multipoint topology, you must configure the master Modem’s DIP switches
differently than those of the slave Modems. Here are the proper DIP-switch settings
for a star topology:
Switch Number 1 2 3 4 5 6 7
Master Positions ON ON ON OFF OFF OFF OFF
Slave Positions ON ON ON OFF OFF OFF ON
4.3 RS-232 Connection
To connect the Modem to a piece of data terminal or data communications
hardware, use a straight-through RS-232 cable. Plug the cable directly into the
DB25 port on the rear of the Modem.
The DCE/DTE switches eliminate the need for a crossover cable.

15
CHAPTER 5: Operation
5. Operation
Once you have configured each Async Short-Haul Modem MP properly and
connected it, simply plug in the AC power adapter to get it running; there is no
power switch on the Modem. You can monitor the Modem’s operation using the
front-panel LED indicators and built-in loopback test modes.
5.1 LED Indicators
The Modem incorporates six front-panel LEDs that show status:
• The power LED lights when AC power is applied to the modem.
• The loopback test LED lights when the loopback test switch has been pressed
and is in a test mode.
• The tri-state TD and RD indicators blink red and green with data activity. Solid
red indicates a low RS-232 logic level and no color indicates no activity on the
line. Note: RS-232 devices idle in a low state, so the LED will glow red if the
connections are correct and the RS-232 device is in an idle state.
• The control in and control out indicators light red for a "low" signal and green
for a "high" signal. The specific pin number associated with these indicators
will vary according to the switch settings you have selected (see Chapter 3).
5.2 Loopback Test Modes
Select the test modes by pressing the Loopback Test switch. When the Modem is in
loopback mode, the Loopback Test LED will glow red. Two tests are possible using
this switch: Local Analog Loop (LAL) and Remote Analog Loop (RAL).
5.2.1 L OCAL A NALOG L OOP
The first test mode is Local Analog Loop (V.54 Loop 3). Any data sent to the local
Modem in this mode will be echoed back (returned) to the user device. For
example, characters typed on the keyboard of a terminal will appear on the
terminal screen (see Figure 5-1 on the following page). If characters are not
echoed back, check the connections between the user device and the Modem.
Wire the units according to the instructions in Chapter 4.

16
ASYNC SHORT-HAUL MODEM MP
5.2.2 R EMOTE A NALOG L OOP
The second test mode is Remote Analog Loop. It causes any characters sent from
the remote Modem to the local Modem to be returned to the remote device (see
Figure 5-1).
Start the test by pressing the Test button on one of the Modems. Then send data
from the other Modem (which must be in normal operating mode). If the data is
echoed back to the Modem in normal mode (for example, if characters you type
appear on your screen), the link to the Modem in loopback mode is working.
NOTE
Only the one Modem should be in test mode. The other Modem should
be in “normal” operating mode or the test will not work.
If no characters are echoed back, check the wiring between the two Modems. Wire
the Modems according to the instructions in Chapter 4.
Figure 5-1. Loopback Test Modes.
RD
TD
TD
RD
Local 1060
In Normal Mode
Remote 1060
In Normal Mode
TX+
TX-
RX-
RX+
RX+
RX-
TX-
TX+
RD
TD
TD
RD
Local 1060
In Loopback Mode
Remote 1060
In Normal Mode
RX+
RX-
TX-
TX+
TX+
TX-
RX-
RX+
Local Modem
In Normal Mode
Remote Modem
In Normal Mode
Local Modem
In Loopback Mode Remote Modem
In Normal Mode

17
CHAPTER 6: Troubleshooting
6. Troubleshooting
Symptom: TD and RD LEDs indicate activity, but units will not communicate
or data is garbled.
Problem 1: Improper RS-232 wiring.
Solution 1: Check wiring between the Modem and connected serial device—it
should be straight through.
Problem 2: Improper twisted-pair wiring.
Solution 2: Compare your twisted-pair wiring with the diagram in Chapter 4.
Problem 3: Improper bit-rate setting.
Solution 3: Make sure the bit rates on all connected serial devices are the
same.
Symptom: TD and RD LEDs indicate activity, but CD LED is unlit or red
(should be green).
Problem 1: Defective twisted-pair line.
Solution 1: Test continuity of the twisted-pair line.
Problem 2: Poor twisted-pair connections to Modems.
Solution 2: Check screw terminal/RJ-11 connections to Modems; check
integrity of plug RJ-11 terminations.
Symptom: Occasional data errors.
Problem 1: Distance/bit-rate capacity exceeded.
Solution 1: Check specifications in Appendix A.
Problem 2: Poor-quality twisted-pair circuit.
Solution 2: Use a different twisted-pair circuit if available.
Problem 3: Poor twisted-pair connections to Modems.
Solution 3: Check screw-terminal/RJ-11 connections to Modems; check
integrity of plug RJ-11 terminations.

18
ASYNC SHORT-HAUL MODEM MP
Symptom: LEDs do not light when the AC power transformer is plugged into
the wall outlet.
Problem 1: The AC transformer is not plugged into the Modem.
Solution 1: Plug in the transformer.
Problem 2: Loose power connection.
Solution 2: Make sure the AC connection is flush.
Problem 3: Outlet is defective.
Solution 3: Try a different outlet.
Problem 4: AC power adapter is defective.
Solution 4: Call for a replacement adapter.
Symptom: No data transfer in either or both directions.
Problem 1: Improper twisted-pair wiring.
Solution 1: Compare your twisted-pair wiring with the diagram in Section 4.1.
Problem 2: Improper DCE/DTE setting.
Solution 2: Set both DCE/DTE switches alike, according to the instructions in
Section 3.2.
Problem 3: Improper bit-rate setting.
Solution 3: Be sure all bit-rate settings on all connected serial ports are the
same.
Problem 4: Improper “control input” pin setting.
Solution 4: The transmitter must be enabled by a specific “control input” pin
(refer to Table 3-1 in Section 3.3).
Problem 5: Distance specifications exceeded.
Solution 5: Check specifications in Appendix A.

19
APPENDIX A: Cable Recommendations
Appendix A. Cable
Recommendations
The Async Short-Haul Modem MP is designed and tested to communicate over
twisted-pair cable that has the following characteristics:
Wire Gauge Capacitance Resistance
19 AWG 83 nF/mi. or 15.72 pF/ft. 0.0163 Ω/ft.
22 AWG 83 nF/mi. or 15.72 pF/ft. 0.0326 Ω/ft.
24 AWG 83 nF/mi. or 15.72 pF/ft. 0.05165 Ω/ft.
Using the characteristics above as a baseline, we estimate the distance limitations
for the Modem to be as follows.
Async Short-Haul Modem MP Distance Table in Miles (km)
Data Wire Gauge
Rate 19 (0.9 mm) 22 (0.5 mm) 24 (0.4 mm)
115,200 1.8 (2.9) 0.75 (1.2) 0.38 (0.6)
57,600 2.5 (4) 1.3 (2.1) 0.95 (1.5)
38,400 3.7 (6) 1.5 (2.4) 1.33 (2.1)
19,200 4.17 (6.7) 1.9 (3.1) 1.42 (2.3)
9600 5.41 (8.7) 2.6 (4.2) 2.08 (3.3)
4800 7.05 (11.3) 3.8 (6.1) 2.84 (4.6)
2400 11.5 (18.5) 7 (11.3) 4.83 (7.8)
1200 14 (22.5) 8.5 (13.7) 5.68 (9.1)
To reduce the potential of difficulties in the field, we recommend that the cable
used to connect the Modem have a capacitance of no greater than 20 pF/ft., and that
the wire be no thinner than 26 AWG.
The Async Short-Haul Modem MP is designed to withstand normal environmental
noise and conditions. However, other environmental factors too numerous to
discuss may affect proper operation.
NOTE
The distance table above should be used as a general guideline only.