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5902 Bell 202 Modem Hardware Manual 
October 19, 2007 

 

23 

5 

Operation 

The 5902 Bell 202T modem operates in full duplex on four wire networks, or in half duplex on two 
or four wire networks, and radios. This section describes how these modes differ in operation. 

5.1 

Full Duplex 

When the modem is configured for full duplex, a carrier is continuously transmitted, and the 
receiver is continuously enabled. This mode is usually used when two modems are connected back-
to-back over a four wire network. This mode is also used by a constant-carrier master modem that 
communicates with multi-dropped slave modems over a four wire network. Full duplex or constant 
carrier operation requires a four wire network. 

5.2 

Half Duplex 

When the modem is configured for half duplex, its transmitter is turned on only when the modem 
transmits data. This mode is always used on two wire networks, and radios. Multi-dropped slaves in 
a four wire network also use this mode. The important characteristic of half duplex is that the 
transmitter shuts off when the modem is not transmitting data. This allows multiple modems to share 
a communication medium. 

Half duplex operation requires that the DTE use RTS/CTS handshaking. When the DTE wishes to 
transmit data, it asserts RTS and wait for the modem to assert CTS before transmitting data. When 
the DTE has finished transmitting, it de-asserts RTS to allow the modem to return to the receiver 
enabled state. 

Note: 

This is not the RTS/CTS handshaking method used by some personal computer 
communication software. Some PC SCADA packages use this handshaking method. Consult 
the description of RTS/CTS handshaking for the product you wish to use. 

In half duplex, switched carrier operation, the modem receiver is disabled during transmission. This 
prevents the modem from receiving its own transmission on a two wire network. 

In half duplex, constant carrier operation, the modem receiver is always enabled. This permits the 
constant carrier master modem to transmit data to slave modems, even if one of the slave modems is 
simultaneously transmitting to the master. 

5.2.1 

Timing Diagrams 

The three timing diagrams below indicate the sequence of operations for receiving and transmitting 
data. 

Summary of Contents for 5902

Page 1: ...2 Modem Hardware Manual CONTROL MICROSYSTEMS SCADA products for the distance 48 Steacie Drive Telephone 613 591 1943 Kanata Ontario Facsimile 613 591 1022 K2K 2A9 Technical Support 888 226 6876 Canada 888 2CONTROL ...

Page 2: ...eleSAFE 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 ...

Page 3: ...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 Clea...

Page 4: ...s 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...

Page 5: ...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 Transm...

Page 6: ...al 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...

Page 7: ...s 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 equipm...

Page 8: ...es 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 mauvai...

Page 9: ...ecified 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...

Page 10: ...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 t...

Page 11: ...SR 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 vo...

Page 12: ...n 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 ra...

Page 13: ... 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 te...

Page 14: ...e 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 ...

Page 15: ... 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 ...

Page 16: ... 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 ...

Page 17: ...e 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 ...

Page 18: ...ower 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 Mo...

Page 19: ...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 rep...

Page 20: ...DX 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 mod...

Page 21: ...es anti streaming in full duplex operation 4 5 5 Soft Carrier Turn off Switches SC0 and SC1 control the length of the soft carrier turn off SCT tone There are four options SCT Tone Length 1 ms No Tone 13 ms 25 ms 38 ms SC0 switch open closed open closed SC1 switch open open closed closed The modem can transmit a soft carrier turn off SCT tone to inform receiving modems to turn off their receivers ...

Page 22: ...er to section 4 5 1 RTS CTS Delay and 4 5 3 Carrier Detect Delay sections for details CARRIER SOURCE AUDIO ONLY AUDIO AND RCD INPUT RCD switch Open closed The modem hardware detects audio energy within specific frequency bands as a received carrier If the audio input is obtained from an unsquelched radio receiver the resulting noise causes false data reception The radio carrier detect option confi...

Page 23: ...f received Radio carrier detect is ignored 4 5 8 1 Constant Carrier Networks Constant carrier operation is often used with multi point networks A full duplex master modem connects to multi dropped half duplex slave modems The master modem always transmits a carrier which is why the system is known as a constant carrier network The main benefits are faster operation the slave modems do not experien...

Page 24: ...the transmitter shuts off when the modem is not transmitting data This allows multiple modems to share a communication medium Half duplex operation requires that the DTE use RTS CTS handshaking When the DTE wishes to transmit data it asserts RTS and wait for the modem to assert CTS before transmitting data When the DTE has finished transmitting it de asserts RTS to allow the modem to return to the...

Page 25: ...on and radio is keyed 1 10 ms after SCT reception stops 4 CTS is asserted by modem after expiration of RTS CTS delay Data transmission starts 5 CTS is held true by modem and carrier continues to be transmitted for CTS hold time after last character is transmitted and RTS returns to false 6 Soft carrier turnoff tone is transmitted for SCT time 7 Radio is de keyed and SCT tone is turned off Modem is...

Page 26: ... for next reception or transmission marks 3 5 4 7 Figure 14 Receive Timing without Soft Carrier Turn off RF Carrier Detect RCD Received Signal Carrier Detect DCD Received Data data 1 2 3 Sequence of Operation 1 Sender keys radio and begins transmitting carrier 2 Carrier is received after radio key up and propagation delays 3 Carrier detect delay starts timing at carrier reception 4 Sender starts t...

Page 27: ...l duplex must be selected TST Open Close switch to engage loop back test 5 3 2 Full Duplex Constant Carrier Master Use this configuration for a master modem connected to one or more slave modems on a multi dropped four wire network This configuration is essentially a full duplex modem except that the carrier detect and carrier loss delays need adjustment since the slave transmitters are turning on...

Page 28: ...n delays in the communication system CL0 CL1 closed closed These switches must be closed for constant carrier reception AS0 AS1 adjust Add anti streaming as required to protect the network against excessive transmission length The maximum message length determines anti streaming time SC0 SC1 closed open Use the shortest SCT time that prevents carrier turn off noise This will normally be achieved w...

Page 29: ...rter delay once communication works If the received signal is weak or the CD led flickers off restore this setting Carrier loss delay will not protect against data loss but can prevent a jittery DCD signal AS0 AS1 adjust Add anti streaming as required to protect the network against excessive transmission length The maximum transmission length determines the anti streaming time SC0 SC1 closed close...

Page 30: ...col If too many errors are experienced increase the RTS CTS delay of both modems If this does not correct the problem increase the carrier detect delay of both modems Ensure that the carrier detect delay is less than the RTS CTS delay of the other modem 5 3 6 Normal Speed Connection to TeleSAFE RTU Use this configuration to connect to a TeleSAFE 6000 or TeleSAFE 6000 16EX RTU with a model 6902 mod...

Page 31: ...ld time or Soft Carrier Turn off transmission Depending on the specific application it may be possible to eliminate these times without causing data errors 5 4 System Configuration Procedures The sample configurations described above work with most systems Use the configuration procedures below to help get a new communication system installed and functional There is a procedure for point to point ...

Page 32: ...Half Duplex Multi Point Systems Unless noted otherwise all switch settings apply to all modems 1 Wire the system as it will be used in the field as described in section 4 2 Field Wiring 2 Set the 2W and 4W switches according to the number of wires used 3 Set the FDX switch according to the system configuration you have chosen See the sample configurations above for suggestions 4 Close the RCD swit...

Page 33: ...tion by reducing clear to send CSH hold soft carrier turn off SCT and RTS CTS delays as described below 12 You can attempt to speed up communication by reducing the clear to send CSH hold and soft carrier turn off SCT delays Open the CSH switch If the system still functions well open the SC0 switch If it still functions well close the SC0 switch and open the SC1 switch Most systems need only the S...

Page 34: ...is no pattern in the location of the bad data A high error rate usually indicates a poor signal to noise ratio a weak signal that is too close to the carrier detect threshold or a signal which is far too strong A high error rate can also indicate interference especially with radio systems Telephone systems sometimes are noisier when the weather is poor Try to increase the signal level if it is low...

Page 35: ...es not work decrease the carrier detect delay on the receiver This problem can occur is the signal level is too low Check the level by putting the modem into the tone transmission test mode see section 6 2 Modem Test Modes The receiving modem s CD LED should be on and its RX LED should blink as data is received If necessary adjust the modem transmit level TX GAIN to get a steady CD at the receivin...

Page 36: ...not used adjust CL0 and CL1 The modem will not allow transmission until carrier is absent unless configured for constant carrier operation If soft carrier turn off is used increase the RTS CTS delay to transmit a pause between carrier start and data transmission 5 5 10 CD LED Always On in Master Modem The carrier detect CD output of a constant carrier modem is always on even though slave modems ar...

Page 37: ... RD LED off a modem on the network is continuously transmitting That modem is improperly configured for full duplex or its DTE device is continuously asserting RTS 5 6 LED Indicators The 5902 modem has seven status LEDs The LEDs are powered by the communication or SCADA controller module through the I O bus The LEDs can be disabled to conserve power Refer to the controller manual for more informat...

Page 38: ... CTS and DSR signals to the DTE It ignores the RTS and DTR signals from the DTE The DCD signal to the DTE follows the state of the CD LED This means the DTE can use a three wire RS 232 interface consisting of TxD RxD and ground No other signals are necessary The buffer capacity of 64 bytes allows the model 5902 to receive approximately 0 5 seconds of data transmission from the DTE before the data ...

Page 39: ... interval will corrupt the preceding message since the character is assumed to be part of the message If a noise character is received after the 29 2 millisecond framing interval the preceding message will not be affected but the character itself may be interpreted as a new Modbus message This extra message may cause problems with some personal computer software TeleSAFE and SmartWIRE RTUs handle ...

Page 40: ...the received carrier actually disappear unless the modem is in half duplex constant carrier mode or the modem receiver will be permanently disabled For this reason the M Option is not recommended for both ends of a full duplex link Since carrier is never turned off the M Option is not needed anyway The M Option is intended for use in a half duplex switched carrier or constant carrier system ...

Page 41: ...dio input level adjustment to adjust the signal where this is possible Where this is not possible lower the 5902 modem transmit level The transmit level is calibrated with a 600 ohm load If there is no load on the transmit output the level is 6 dB 2 times higher Thus the factory adjusted level is 6 dBm with no load Connect a 600 ohm resistor across the output to lower the level by 6 dB 6 1 1 1 0 d...

Page 42: ...ion 6 2 1 2 RCD and KEY Test The CD LED shows the status of the RCD input If the RCD input is true the CD LED will illuminate The KEY output is set to the same state as the KEY led A good way test the RCD input and KEY output is Wire the KEY output to the RCD input Toggle any configuration switch to cause the KEY LED and output to toggle Observe that the RCD input LED is changes states when the KE...

Page 43: ...the configuration switches and will immediately begin operation 6 2 3 Full Duplex Loop Back Test This test confirms that the modem receiver transmitter and network wiring are functioning properly in a four wire full duplex point to point system To select this test mode Apply power to the modem Close the FDX switch select full duplex mode Close the TST switch Any data which received by the modem on...

Page 44: ...port transmit data to the modem The data should be echoed back by the modem The transmit output can be connected to the receive input in two ways Select 2 wire operation to loop the signal back internally Close the 2 WIRE switch and open the 4 WIRE switch This does not test the line isolation transformers Select 4 wire operation to loop the signal back externally Open the 2 WIRE switch and close t...

Page 45: ...3 dBm potentiometer adjustable to 40 dBm Output Impedance 600 ohm balanced transformer isolated Input Impedance 600 ohm balanced transformer isolated Anti Streaming none 10Sec 30Sec 60Sec RTS CTS Delay wire 25ms 50ms 125ms 250ms radio 67ms 133ms 266ms 1000ms CTS Hold Time 1ms 8ms Soft Carrier Tone Transmit Time none 13ms 25ms 38ms Soft Carrier Tone Detect Delay 4ms to 10ms Carrier Detect Delay wir...

Page 46: ...stic test Power Requirements Model 5902 5V at 60mA Model 5902SA 115 VAC at10 VA Field Termination 8 pole removable terminal block 12 to 22 AWG 15 amp contacts RJ 45 modular jack Dimensions 4 25 inch 108 mm wide 4 625 inch 118 mm high 1 75 inch 44 mm deep Mounting Model 5902 7 5 x 35 DIN rail Model 5902SA desktop rubber feet Packaging Corrosion resistant zinc plated steel with black enamel paint En...

Page 47: ...5902 Bell 202 Modem Hardware Manual October 19 2007 46 8 Approvals and Certifications Safety Non Incendive Electrical Equipment for Use in Class I Division 2 Groups A B C and D Hazardous Locations ...

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