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Documentation Number 485T1995 Manual

5

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 433-5105

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Summary of Contents for 485T

Page 1: ... product Designed and Manufactured In Ottawa Illinois USA of domestic and imported parts by B B Electronics Mfg Co Inc 707 Dayton Road P O Box 1040 Ottawa IL 61350 PH 815 433 5100 FAX 815 433 5105 Internet http www bb elec com orders bb elec com support bb elec com 1992 B B Electronics Revised August 1992 Not Recommended for New Installations Please contact Technical Support for more information ...

Page 2: ...3 5105 TABLE OF CONTENTS INTRODUCTION 1 RS 422 AND RS 485 STANDARDS 1 CONTROLS AND CONNECTIONS ON THE 485T 6 A AND B TERMINALS 6 GROUND TERMINAL 6 THRESHOLD POT 7 POSITIVE THRESHOLD EXCEEDED LED 7 NEGATIVE THRESHOLD EXCEEDED LED 7 RS 422 RS 485 SWITCH 8 TERMINATION SWITCH 8 POWER 8 RS 232 DATA OUT CONNECTOR 8 RS 422 485 TEST 9 ...

Page 3: ...re usually located close to each other wire length was not much of a factor in the standard RS 232 maximum wire lengths were set at 50 feet RS 232 lines can run farther with special low capacitance wire but there is a practical limit of 300 or so feet The EIA then developed two newer standards to allow serial data communications to go past the 50 foot barrier The first is RS 422 Electrical Charact...

Page 4: ...a Typically the RS 422 or RS 485 driver will switch between 5 volts and ground Since devices can be long distances apart they can be powered on different power lines or transformers that can force their reference grounds to be at different voltages The RS 422 Standard allows the signal lines to go as high as 7 volts and as low as 7 volts The RS 485 Standard allows 12 volts and 7 volts Another requ...

Page 5: ...Documentation Number 485T1995 Manual 3 B B Electronics PO Box 1040 Ottawa IL 61350 PH 815 433 5100 FAX 815 433 5105 ...

Page 6: ...4 Documentation Number 485T1995 Manual B B Electronics PO Box 1040 Ottawa IL 61350 PH 815 433 5100 FAX 815 433 5105 ...

Page 7: ...Documentation Number 485T1995 Manual 5 B B Electronics PO Box 1040 Ottawa IL 61350 PH 815 433 5100 FAX 815 433 5105 ...

Page 8: ...m as two separate networks You would first run your tests on one pair of signal lines and then run them again on the other pair NOTE Make sure that you are connected to the correct two lines when using the tester It is possible for the tester to look like it is working properly when one line is connected and the other is floating or connected to a wire in another pair Ground Terminal The GND termi...

Page 9: ...d make the lower voltage readings difficult to read Readings above 1 volt indicate that differential voltage is more than adequate Positive Threshold Exceeded LED The RS 422 Standard states that a network should not have a positive common mode voltage of more than 7 volts This means that the difference between Signal Ground and either the A or B input should not be more than positive 7 volts For R...

Page 10: ...network with no terminations and want to see what happens if you terminate it at one point Normally you should leave this switch OFF down Power The 485T will work from a nine volt battery or from 12 VDC through the 2 5 mm jack marked DC Power 12VDC IN When you plug in the external power supply available from B B Electronics as the Model 485PS the battery is automatically disconnected RS 232 Data O...

Page 11: ...g sent and when the network is idle If either of these LEDs is on or blinking you may have a grounding problem You should first check that the RS 422 RS 485 switch is in the proper position and that the Signal Ground is connected correctly to the 485T Refer to B B Electronics free RS 422 485 Application Note for information on proper grounding of your network NOTE If the positive or negative thres...

Page 12: ...olt Most RS 422 485 drivers start out with a differential of about 2 volts but the resistance inductance and capacitance in the line can reduce it considerably NOTE The differential voltage you are trying to measure is the RECEIVED voltage You should only make the threshold measurement when the node you are testing is RECEIVING data not when it is transmitting If you have a multiple node system wi...

Page 13: ... for handshake loopback Pin 7 is ground and there is no connection to pin 3 NOTE If the data you receive is garbled you may have the A B connectors backwards Try reversing them With the 485T connected and the THRESHOLD pot turned to zero full clockwise any RS 422 485 data on the network will appear as RS 232 data at pin 2 of the RS 232 DATA OUT jack If you have a four wire network you can only vie...

Page 14: ...12 Documentation Number 485T1995 Manual B B Electronics PO Box 1040 Ottawa IL 61350 PH 815 433 5100 FAX 815 433 5105 ...

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