Bell 5902 User manual

5902 Bell 202 Modem
Hardware Manual
CONTROL
MICROSYSTEMS
SCADA products... for the distance
48 Steacie Drive Telephone: [phone]
Kanata, Ontario Facsimile: 613-591-1022
K2K 2A9 Technical Support: 888-226-6876
Canada 888-2CONTROL

5902 Bell 202 Modem Hardware Manual
October 19, 2007
1
5902 Bell 202 Modem Hardware Manual
©2000 - 2006 Control Microsystems Inc.
All rights reserved.
Printed in Canada.
Trademarks
TeleSAFE, TelePACE, SmartWIRE, SCADAPack, TeleSAFE Micro16 and
TeleBUS are registered trademarks of Control Microsystems Inc.
All other product names are copyright and registered trademarks or trade names
of their respective owners.
Material used in the User and Reference manual section titled SCADAServer
OLE Automation Reference is distributed under license from the OPC
Foundation.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
2
Table of Contents
1OVERVIEW.................................................................................................... 5
2INDUSTRY CANADA CERTIFICATION........................................................ 6
3IMPORTANT SAFETY INFORMATION......................................................... 8
4INSTALLATION............................................................................................. 9
4.1 Connecting the Modem.................................................................................. 9
4.2 Field Wiring..................................................................................................10
4.2.1 RS-232 Serial Port..................................................................................10
4.2.2 Terminal Block........................................................................................12
4.2.3 RJ-45 Modular Jack................................................................................12
4.3 Connecting to Dedicated Lines....................................................................12
4.3.1 Four wire mode....................................................................................... 12
4.3.2 Two wire mode ....................................................................................... 13
4.4 Connecting to a Radio ................................................................................. 16
4.4.1 Modem Transmitter Output.....................................................................16
4.4.2 Modem Receiver Input............................................................................16
4.4.3 Key Output.............................................................................................. 16
4.4.4 Radio Carrier Detect Input......................................................................16
4.4.5 Wiring Diagrams.....................................................................................16
4.5 Configuration Switches ................................................................................18
4.5.1 RTS/CTS Delay...................................................................................... 18
4.5.2 Carrier Detect Delay ............................................................................... 19
4.5.3 Carrier Loss Delay..................................................................................19
4.5.4 Anti-Streaming........................................................................................20
4.5.5 Soft Carrier Turn-off................................................................................20
4.5.6 Clear-to-Send Hold Time........................................................................21
4.5.7 Radio Carrier Detect............................................................................... 21
4.5.8 Duplex .................................................................................................... 22
4.5.9 Test Mode Selection............................................................................... 22
5OPERATION................................................................................................ 23
5.1 Full Duplex...................................................................................................23

5902 Bell 202 Modem Hardware Manual
October 19, 2007
3
5.2 Half Duplex .................................................................................................. 23
5.2.1 Timing Diagrams..................................................................................... 23
5.3 Sample Configurations................................................................................. 26
5.3.1 Full Duplex Back-to-Back Modems.........................................................26
5.3.2 Full Duplex Constant Carrier Master.......................................................26
5.3.3 Half Duplex Slave for Constant Carrier Master....................................... 27
5.3.4 Half Duplex Master Or Slave .................................................................. 28
5.3.5 High Speed Connection to TeleSAFE RTU............................................28
5.3.6 Normal Speed Connection to TeleSAFE RTU........................................29
5.4 System Configuration Procedures ............................................................... 30
5.4.1 Full Duplex Point-to-Point Systems ........................................................ 31
5.4.2 Half Duplex Multi-Point Systems ............................................................31
5.5 Common Problems and Solutions ............................................................... 33
5.5.1 RTS Always On in Half Duplex............................................................... 33
5.5.2 High Error Rate....................................................................................... 33
5.5.3 Modem Receives Data but Never Transmits..........................................34
5.5.4 Other Modems Do Not Receive Data .....................................................34
5.5.5 Bad Data at Start of Message................................................................. 34
5.5.6 Bad Data after End of Message ............................................................. 34
5.5.7 Missing End of Long Message................................................................35
5.5.8 RS LED Always On; All Other LEDs Off................................................. 35
5.5.9 DTE Transmits Too Soon after Receive................................................. 35
5.5.10 CD LED Always On in Master Modem....................................................35
5.5.11 CD LED Always On in Radio System .....................................................36
5.5.12 CD LED Always On in 2 Wire System ....................................................36
5.6 LED Indicators ............................................................................................. 36
5.7 F Option.......................................................................................................37
5.7.1 Supported Communication Parameters..................................................37
5.8 M Option ......................................................................................................38
5.8.1 Carrier Turn Off and the Modbus RTU Protocol.....................................38
5.8.2 M Option Operation ................................................................................ 38
6MAINTENANCE........................................................................................... 40
6.1 Gain Adjustments.........................................................................................40
6.1.1 Transmitter Adjustment .......................................................................... 40
6.1.2 Receiver Adjustment...............................................................................40
6.2 Modem Test Modes ..................................................................................... 40

5902 Bell 202 Modem Hardware Manual
October 19, 2007
4
6.2.1 Basic Functional Test ............................................................................. 41
6.2.2 Tone Transmission Test......................................................................... 41
6.2.3 Full Duplex Loop Back Test....................................................................42
6.3 Troubleshooting ...........................................................................................42
7SPECIFICATIONS....................................................................................... 44
8APPROVALS AND CERTIFICATIONS ....................................................... 46
Index of Figures
Figure 1: 5902 Module Layout............................................................................................. 9
Figure 2: RS-232 Port Connector (DCE)............................................................................10
Figure 3: RS-232 Wiring - 5902 (DCE) to DTE ..................................................................11
Figure 4: Four Wire Network..............................................................................................13
Figure 5: Two Wire Network ..............................................................................................13
Figure 6: Four Wire RJ-45 Connection...............................................................................14
Figure 7: Two Wire RJ-45 Connection...............................................................................14
Figure 8: Four Wire Terminal Block Connection.................................................................15
Figure 9: Two Wire Terminal Block Connection.................................................................15
Figure 10: Typical Connection to Maxon Radio..................................................................17
Figure 11: Typical Connection to Johnson Radio...............................................................17
Figure 12: Typical Connection to Motorola Radio...............................................................17
Figure 13: Transmit Timing with Soft Carrier Turnoff .........................................................24
Figure 14: Receive Timing without Soft Carrier Turn-off ....................................................25
Figure 15: Receive Timing with Soft Carrier Turn-off .........................................................25

5902 Bell 202 Modem Hardware Manual
October 19, 2007
5
1 Overview
The model 5902 Bell 202 modem converts RS-232 signal levels to audio tones for transmission over
radios, two wire networks, four wire multi-point networks, and four wire point-to-point networks.
The modem is transformer isolated from the communication system, so it is well suited to
applications which may experience high voltage transients, static discharges, or high common-mode
voltages.
The 5902 modem is compatible with virtually all types of radio transceivers. Radio communication
is facilitated by an isolated radio transmitter key output, and a radio frequency carrier detect input.
The input can be used to inhibit transmission if a radio signal is detected. Each signal can be wired
for active high or active low signals. Configurable carrier detect and loss delays, and RTS/CTS
delays provide high quality communication in a broad variety of environments.
Multi-point telephone and radio applications are protected against inadvertent sustained
transmission through a user selected anti-streaming timer. This feature prevents a continuously
keyed modem from swamping the communication system.
Configuration switches permit adjustment of carrier detection and loss delays, anti-streaming time,
soft-carrier turn-off tones, RTS/CTS handshake timing, and full/half duplex selection. Self test and
adjustment modes facilitate field maintenance.
Two package versions are available. The model 5902 modem is a DIN rail mounted version for
SmartWIRE TeleSAFE Micro16 and SCADAPack controllers. The model 5902SA is a desktop
version for with personal computers and other RS-232 equipment. This manual covers the 5902
modem.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
6
2 Industry Canada Certification
The model 5902 modem is registered with Industry Canada as complying with standard CS02. The
certification number is on a sticker attached to the unit. Industry Canada requires that the following
information be conveyed to the user.
NOTICE: The Industry Canada label identifies certified equipment. This certification means
that the equipment meets certain telecommunications network protective,
operational and safety requirements. Industry Canada does not guarantee the
equipment will operate to the user’s satisfaction.
Before installing this equipment, users should ensure that it is permissible to be connected to the
facilities of the local telecommunications company. The equipment must also be installed using an
acceptable method of connection. The customer should be aware that the compliance with the above
conditions may not prevent degradation of service in some situations.
Repairs to certified equipment should be made by an authorized Canadian maintenance facility
designated by the supplier. Any repairs or alternations made by the user to this equipment, or
equipment malfunctions, may give the telecommunications company cause to request the user to
disconnect the equipment.
Users should ensure for their own protection that the electrical ground connections of the power
utility, telephone lines and internal metallic water pipe system, if present, are connected together.
This precaution may be particularly important in rural areas.
CAUTION: Users should not attempt to make such connections themselves, but should contact
the appropriate electric inspection authority, or electrician, as appropriate.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
7
AVIS: L’étiquette de l'Industrie Canada identifie le matériel homologué. Cette étiquette certifie
que le matériel est conforme à certaines normes de protection, d’exploitation et de sécurité
des réseaux de télécommunications. Industrie Canada n’assure toutefois pas que le
matériel fonctionnera à la satisfaction de l’utilisateur.
Avant d’installer ce matériel, l’utilisateur doit s’assurer qu’il est permis de le raccorder aux
installations de l’entreprise locale de télécommunication. Le matériel doit également être installé en
suivant une méthod acceptée de raccordement. L’abonné ne doit pas oublier qu’il est possible que la
conformité aux conditions énoncées ci-dessus n’empêchent pas la dégradation du service dans
certaines situations.
Les réparations de matériel homologué doivent être effectuées par un centre d’entretien canadien
autorisé, désigné par le fournisseur. La compagnie de télécommunications peut demander à
l’utilisateur de débrancher un appareil à la suite de réparations ou de modifications effectuées par
l’utilisateur ou a cause de mauvais fonctionnement.
Pour sa propre protection, l’utilisateur doit s’assurer que tous les fils de mise à la terre de la source
d’énergie électrique, les lignes téléphoniques et les canalisations d’eau métalliques, s’il y en a, sont
raccordés ensemble. Cette précaution est particulièrement importante dans les régions rurales.
AVERTISSEMENT: L’utilisateur ne doit pas tenter de faire ces raccordements lui-même; il doit
avoir recours à un service d’inspection des installations électriques, ou à
un électricien, selon le cas.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
8
3 Important Safety Information
Power, input and output (i/o) wiring must be in accordance with Class I, Division 2 wiring methods
Article 501-4 (b) of the National Electrical Code, NFPA 70 for installations in the U.S., or as
specified in Section 18-1J2 of the Canadian Electrical Code for installations within Canada and in
accordance with the authority having jurisdiction.
WARNING !
EXPLOSION HAZARD - SUBSTITUTION OF COMPONENTS MAY
IMPAIR SUITABILITY FOR CLASS 1, DIVISION 2.
WARNING !
EXPLOSION HAZARD –WHEN IN HAZARDOUS LOCATIONS, TURN
OFF POWER BEFORE REPLACING OR WIRING MODULES.
WARNING !
EXPLOSION HAZARD - DO NOT DISCONNECT EQUIPMENT
UNLESS POWER HAS BEEN SWITCHED OFF OR THE AREA IS
KNOWN TO BE NONHAZARDOUS.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
9
4 Installation
The installation of the 5902 modem requires mounting the modem on the 7.5mm by 35mm DIN rail
and connecting the 5902 modem to the system I/O Bus. Refer to the System Configuration Guide,
at the beginning of this manual, for complete information on system layout, I/O Bus cable routing
and 5902 modem installation.
4.1 Connecting the Modem
The 5902 modem is normally connected to the SCADAPack I/O Bus through the I/O Bus
Connectors as shown in figure 1.In this configuration the SCADAPack provides a modem reset
(/RST) signal and a signal to enable the leds (LEDON) on the 5902 modem.
The 5902 modem is also available in a stand alone (SA) configuration. In this configuration the
5902 is not connected to a SCADAPack controller and the modem reset (/RST) signal and a signal
to enable the leds (LEDON) on the 5902 modem are not available. Two jumpers, J1 and J2, are
included to enable these signals on the 5902SA modem. Figure 1: 5902 Module Layout shows the
location of the jumpers.
5902 Modem
Remove jumper at J1 (/RST).
Remove jumper at J2 (LEDON).
5902SA Modem
Install jumper at J1 (/RST).
Install jumper at J2 (LEDON).
Status LEDs
I/O Bus
Connector
I/O Bus
Connector
RJ-45 Jack
RS-232 DCE
Connector
+ –
Tx/Rx
Termination
Block
Configuration
Switches
+ –
Rx
+ –
KEY
+ –
RCD
LEDON Jumper (J2)
/RST Jumper (J1)
RX Gain
Adjustment
TX Gain
Adjustment
TX Gain Jumper (J3)
Figure 1: 5902 Module Layout

5902 Bell 202 Modem Hardware Manual
October 19, 2007
10
4.2 Field Wiring
The 5902 modem has three connectors for field wiring.
The RS-232 port is wired to the DE-9S socket connector. Refer to section 4.2.1-RS-232 Serial Port
for more information.
The modem wiring is terminated on either an 8 pole terminal block or an RJ-45 modular jack. The
terminal block is used for radios, private lines and leased telephone lines. The jack is used typically
for telephone lines. Refer to section 4.2.2-Terminal Block and 4.2.3-RJ-45 Modular Jack for more
information.
The modem operates on radios, two wire networks, four wire multi-point networks, and four wire
point-to-point networks. Section 4.3-Connecting to Dedicated Lines describes wiring networks on
dedicated lines. Section 4.4-Connecting to a Radio describes wiring to radios.
4.2.1 RS-232 Serial Port
2
RxD
3
TxD
7
RTS
8
CTS
1
DCD
6
DSR
4
DTR
9
5 V
5
Gnd
Figure 2: RS-232 Port Connector (DCE)
The RS-232 port is a 9-pin female D-sub-miniature connector (DE-9S) configured as Data
Communications Equipment (DCE). A maximum cable length of 50 feet (15.2 m) is allowed. Figure
2: RS-232 Port Connector (DCE) and the table below describe the RS-232 connector.
In the following table a MARK is a voltage of +3 volts or greater; a SPACE is a voltage of –3 volts
or less.
Pin
Type
Description
Pin1
DCD
output
This signal is at a MARK level when carrier is detected by
the modem on the receiver inputs.
The CD led is on for a MARK level.
Pin 2
RxD
output
Data received by the modem is output on this pin. The level
is SPACE on standby and MARK for received data.
The RD LED is lit for a MARK level.
Pin 3
TxD
input
Data transmitted by the modem is input on this pin from the
DTE. The level is SPACE on standby and MARK for
transmitted data.
The TD LED is lit for a MARK level.
Pin 4
DTR
input
This signal indicates that the DTE is ready to receive data.
It is not used by the modem.
Pin 5
Ground
This pin is connected to the I/O system ground.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
11
Pin
Type
Description
Pin 6
DSR
output
This signal indicates the modem is ready to start
communication. It is always in a MARK state.
Pin 7
RTS
input
This input must be a MARK for the modem to transmit
data. The DTE should set it to a MARK just before
transmission of data. The CTS output will be asserted
when the modem is ready to transmit data.
The RS LED is ON for a MARK level.
Pin 8
CTS
output
This output indicates the modem is ready to transmit data.
A MARK level indicates the modem is ready. The DTE
should wait for this signal before transmitting data.
The CS LED is on for a MARK level.
Pin 9
5 Volt
Power
input/
output
This pin is connected to the 5V power supply. It is a power
source for an external device when used as an output. It
powers the modem when used as an input.
This pin must NOT be connected if it is not used.
All RS-232 wiring must use shielded cable. The shield should be connected to chassis ground at one
end of the cable only. The DE-9 connector shell is a good ground point. Failure to properly shield
the cable may result in the installation not complying with FCC or DOC radio interference
regulations.
The 5902 modem is connected typically to a DTE device. Figure 3: RS-232 Wiring - 5902 (DCE)
to DTE shows a typical connection.
The serial cable that is provided with the 5902 modem is suitable for connecting the modem to a
Data Communication Equipment (DCE) device.
DTE
5902 (DCE)
6
9
DCD
RxD
TxD
DTR
GND
RTS
CTS
5 Volt
2
3
4
5
7
8
1
DCD
RxD
TxD
DTR
GND
RTS
CTS
See device
specifications
for pin numbers
Pin 9 is a connected to the 5 Volt
power supply. Use caution when
connecting to this pin.
Figure 3: RS-232 Wiring - 5902 (DCE) to DTE

5902 Bell 202 Modem Hardware Manual
October 19, 2007
12
4.2.2 Terminal Block
Field wiring for radios and dedicated lines connects to the terminal block. It has 8 poles:
Poles 1 and 2 are the transmit pair for 4-wire mode and the transmit/receive for 2-wire mode.
Poles 3 and 4 are the receive pair for 4-wire mode.
Poles 5 and 6 are the radio key output.
Poles 7 and 8 are the radio carrier detect input.
Controller, modem and I/O modules use screw termination style connectors for termination of field
wiring. They accommodate solid or stranded wires from 22 to 12 AWG.
The connectors are removable. This allows module replacement without disturbing the field wiring.
Leave enough slack in the wiring for the connector to be removed.
CAUTION: Remove power before servicing unit.
To remove the connector:
Pull the connector upward from the board. Apply even pressure to both ends of the connector.
To install the connector:
Line up the pins on the module with the holes in the connector. Make sure all the pins line up
properly.
Push the connector onto the pins. Apply even pressure to both ends on the connector.
Refer to section 4.3-Connecting to Dedicated Lines for wiring diagrams for typical networks. Refer
to section 4.4-Connecting to a Radio for wiring diagrams for common radios.
4.2.3 RJ-45 Modular Jack
Field wiring for telephone lines connects to the RJ-45 modular jack. It mates with an 8 pin modular
plug with at least 4 contacts. This type of connector is common in the telephone industry.
Pins 4 and 5 are the transmit pair for 4-wire mode and the transmit/receive for 2-wire mode.
Pins 3 and 6 are the receive pair for 4-wire mode.
Pins 1, 2, 7 and 8 are not used.
Refer to section 4.3- Connecting to Dedicated Lines for wiring diagrams for typical networks.
4.3 Connecting to Dedicated Lines
The 5902 modem operates in full duplex on four wire networks, or in half duplex on two wire
networks. It uses leased telephone lines or private lines.
4.3.1 Four wire mode
Four wire operation uses one pair of wires for transmitting data and a second pair for receiving data.
The transmitting pair are connected to the +TX and –TX. The receiving pair are connected to the
+RX and –RX terminals.
Figure 4: Four Wire Network shows a typical 4 wire network. Figure 6: Four Wire RJ-45
Connection and Figure 8: Four Wire Terminal Block Connection give wiring details.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
13
4.3.2 Two wire mode
Two wire operation uses one pair of wires for transmitting and receiving data. The field wiring
connects to the +Tx/Rx and –Tx/Rx terminals.
Figure 5: Two Wire Network shows a typical 2 wire network. Figure 7: Two Wire RJ-45
Connection and Figure 9: Two Wire Terminal Block Connection give wiring details.
+TX
–TX
–RX
+RX
+TX
–TX
–RX
+RX
+TX
–TX
–RX
+RX
+TX
–TX
–RX
+RX
MASTER
SLAVE
SLAVE
SLAVE
Figure 4: Four Wire Network
--Tx/Rx
+Tx/Rx
--Tx/Rx
+Tx/Rx
--Tx/Rx
+Tx/Rx
--Tx/Rx
+Tx/Rx
MASTER
SLAVE
SLAVE
SLAVE
Figure 5: Two Wire Network

5902 Bell 202 Modem Hardware Manual
October 19, 2007
14
RJ-45 Modular Jack
4 Wire Conections
1. no connection
2. no connection
3. +Rx
4. +Tx
5. –Tx
6. –Rx
7. no connection
8. no connection
Tx pair to slaves
Rx pair from slaves
2
1
8
7
6
5
4
3
Figure 6: Four Wire RJ-45 Connection
RJ-45 Modular Jack
2 Wire Connections
1. no connection
2. no connection
3. no connection
4. +Tx/Rx
5. –Tx/Rx
6. no connection
7. no connection
8. no connection
Tx/Rx pair
2
1
8
7
6
5
4
3
Figure 7: Two Wire RJ-45 Connection

5902 Bell 202 Modem Hardware Manual
October 19, 2007
15
Tx pair to slaves
Rx pair from slaves
1
2
3
4
5
6
7
8
5902 Termination Block
Tx/Rx
+
+
+
+
–
–
–
–
Rx
KEY
RCD
Figure 8: Four Wire Terminal Block Connection
Tx/Rx pair
1
2
3
4
5
6
7
8
5902 Termination Block
Tx/Rx
+
+
+
+
–
–
–
–
Rx
KEY
RCD
Figure 9: Two Wire Terminal Block Connection

5902 Bell 202 Modem Hardware Manual
October 19, 2007
16
4.4 Connecting to a Radio
There are four signals that must be connected for most radios. These signals are described below.
Refer to the manual supplied with your radio for more information.
Wiring diagrams are provided for several common radios. Call Control Microsystems if you require
assistance in connecting a radio not described here.
4.4.1 Modem Transmitter Output
The modem transmitter output connects to the radio transmitter audio input. The modem is factory
calibrated with the transmitter output at 0 dBm. This level is too high for many radios. It is
necessary to reduce the modem output by adjusting the TX GAIN potentiometer (see section 6.1-
Gain Adjustments). The transmitter output can be reduced to a level most radios accept. If
additional attenuation is required, an external resistor voltage divider may be used.
4.4.2 Modem Receiver Input
The modem receiver input connects to the radio receiver data output. The modem is factory
calibrated with the receiver input set to detect signals as low as –30dBm. All radios provide output
signals well above this level, so no adjustment of the RX GAIN potentiometer should be necessary.
4.4.3 Key Output
The KEY output is an optically isolated transistor, which is used to turn on a radio transmitter. It is
referred to as a keyline or PTT (push to talk) signal in radio manuals. The following precautions
must be taken when using the KEY output.
The polarity of the KEY output must be observed.
The output current must be limited to 25mA during the on condition.
The output voltage must be limited to 15 volts during the off condition.
The KEY output is on (capable of conducting current) during transmission of carrier tones and data.
4.4.4 Radio Carrier Detect Input
The Radio Carrier Detect (RCD) input prevents the modem from keying a radio transmitter when RF
carrier is detected. This prevents one radio from transmitting over another. It is highly recommended
that radio applications make use of the RCD input.
The RCD input enables the modem receiver only when a radio frequency carrier is present, when the
RCD switch is closed. This minimizes bad data caused by an unsquelched radio. If a radio does not
squelch its audio, use of the RCD input is mandatory for reliable communication.
4.4.5 Wiring Diagrams
Wiring diagrams are provided for the following radios. Refer to the manual supplied with your radio
for more information.
Maxon DM-0500 Series
E.F. Johnson models 3410/3490
Motorola RNet series

5902 Bell 202 Modem Hardware Manual
October 19, 2007
17
+
10.8 Volts
–
Maxon D Connector
1. data in
2. data out
3. PTT
4. GND
5. Vcc
6. CDS
7. no connection
8. no connection
9. no connection
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
5902 Termination Block
Tx/Rx
+
+
+
+
–
–
–
–
Rx
KEY
RCD
Figure 10: Typical Connection to Maxon Radio
+
–
Johnson Connector Pins
1. no connection
2. no connection
3. no connection
4. no connection
5. B+
6. Keyline (active low)
7. Carrier Detect (active high)
8. Data In
9. Ground
10. Data out
Power
Supply
Johnson models 3410/3490
10 pin connector
1
2
3
4
5
6
7
8
10
9
8
7
6
5
5902 Termination Block
Tx/Rx
+
+
+
+
–
–
–
–
Rx
KEY
RCD
Figure 11: Typical Connection to Johnson Radio
+
----
Motorola Connector Pins
1. Not Used
2. Not Used
3. Not Used
4. Mic Audio Input
5. Channel Select
6. B+
7. Data Input
8. Data Output
9. Not Used
10. Not Used
11. Squelch Disable
12. Audio Output
13. Carrier Detect
14. PTT
15. Ground
Power
Supply
Motorola RNet Series
Telemetry Radio
15 pin D-connector
1
2
3
4
5
6
7
8
8
15
7
13
14
6
5902 Termination Block
Tx/Rx
+
+
+
+
----
----
----
----
Rx
KEY
RCD
Connections shown for:
Carrier detect active high
PTT active low
Channel 1 enabled
Squelch enabled
Figure 12: Typical Connection to Motorola Radio

5902 Bell 202 Modem Hardware Manual
October 19, 2007
18
4.5 Configuration Switches
The 5902 modem has 16 configuration switches. They specify the modem communication
parameters and operating modes. See Figure 1: 5902 Module Layout for switch locations. The
functions are described in detail below.
The switches can be changed with the power applied. All changes take effect immediately.
To CLOSE a switch, press down on the right side of the switch.
To OPEN a switch, press down on the left side of the switch.
CAUTION: Do not use a pencil, mechanical pencil or pen to adjust the switches. Graphite and
ink can cause switch failure. A paper clip is a good tool for adjusting switches.
4.5.1 RTS/CTS Delay
The CS0 and CS1 switches control the RTS/CTS delay. There are four options. The delays are
longer when the RCD option is enabled, as radios usually require longer delays.
DELAY (RCD open)
DELAY (RCD closed)
25 ms
67 ms
50 ms
133 ms
125 ms
266 ms
250 ms
1000 ms
CS0 switch
open
closed
open
closed
CS1 switch
open
open
closed
closed
The RTS and CTS signals coordinate data transmission between the modem and the DTE. When
RTS is asserted by the DTE, the modem turns on its carrier, keys the radio and starts a delay. At the
conclusion of the delay, CTS is asserted by the modem to allow the DTE to transmit data. This delay
has different functions according to the modem duplex setting.
4.5.1.1 Half Duplex (FDX open)
The RTS/CTS delay allows the modem carrier to be transmitted to and be detected by the receiving
modem or modems. The receiving modem requires time to detect and synchronize to the carrier,
before it can accept data. Radios may take some time to key up to full power before transmitting.
Radio repeaters also require time to engage. The RTS/CTS delay provides this time.
When RTS is asserted by the DTE, the 5902 modem closes the KEY output, turns on the transmit
carrier, and starts the delay. When the delay has expired, the modem asserts CTS to allow the DTE
to transmit.
The modem will not transmit carrier or start the RTS/CTS delay, while carrier is being received,
unless constant carrier operation is selected (refer to section 4.5.3-Carrier Loss Delay). This
prevents the modem from transmitting at the same time as another modem.
4.5.1.2 Full Duplex (FDX closed)
The RTS/CTS delay has no effect on modem operation in full duplex mode. The modem always
transmits a carrier.
The RTS/CTS delay is functional and can be used to insert a pause between transmissions. To use
this feature, the DTE device must use RTS/CTS handshaking (half duplex operation). When the
DTE is ready to transmit data, it asserts RTS and waits for CTS to be asserted by the modem. When
CTS is asserted, the DTE transmits the data. The DTE releases RTS at the end of transmission. This
causes a pause before each transmission.

5902 Bell 202 Modem Hardware Manual
October 19, 2007
19
4.5.2 Carrier Detect Delay
The CD0 and CD1 switches control the carrier detect delay. There are four options. The delays are
longer when the RCD option is enabled, as radios usually require longer delays.
DELAY (RCD open)
DELAY (RCD closed)
19 ms
33 ms
30 ms
67 ms
51 ms
133 ms
92 ms
265 ms
CD0 switch
Open
closed
Open
closed
CD1 switch
Open
open
Closed
closed
The modem will not receive data until carrier is detected. The carrier detect period ensures that a
sustained carrier is present, before the receiver is enabled.
The carrier detect delay prevents noise from being received at the beginning of each reception. The
carrier must be present for this period, before it is detected as carrier. If the carrier drops out during
the detect period, it will not be detected as carrier.
NOTE: The carrier detect delay switch settings must be less than the RTS/CTS delay of the
transmitting modem, plus any propagation delays such as radio transmitter and radio
receiver attack times.
4.5.3 Carrier Loss Delay
The CL0 and CL1 switches control the carrier loss delay. There are four options. The duplex (FDX)
switch affects the selection of one option (see section 4.5.8-Duplex).
CL DELAY
(+/–1.5 ms)
6 ms
10 ms
23 ms
39 ms FDX
Constant Carrier HDX
CL0 switch
Open
closed
open
closed
CL1 switch
Open
open
closed
closed
Carrier can be lost in the middle of a transmission, especially with radio communication. The carrier
loss delay allows the carrier to disappear for brief intervals, without the loss causing the modem to
test for the carrier detect delay when the carrier reappears.
The carrier loss delay also determines how long the modem waits after reception terminates, before
it allows transmission in half duplex mode. Therefore, the carrier loss delay is also a transmission
turnaround delay for half duplex mode.
4.5.3.1 Use With Constant Carrier Reception
In constant carrier, half duplex (HDX) mode a carrier signal is continuously received on the receive
pair, Rx + and Rx -. Selecting constant carrier reception mode allows the modem to transmit data on
the transmit pair, Tx/Rx + and Tx/Rx -, even though received carrier is detected. Close switches
CL0 and CL1 when connected to a constant carrier source in a four wire, half duplex system.
4.5.3.2 Use With Full Duplex
The carrier loss delay always functions in full duplex mode (see section4.5.8-Duplex). The constant
carrier option is not available, since the modem can transmit at any time when in full duplex.