RS-422/RS-485 Switch
This switch controls the positive threshold voltage for the Positive Threshold LED only. When the switch is in the RS-422 position, the positive threshold is +7 volts. When it is in the RS-485 position, the positive threshold is +12 volts. This switch has no effect on the Data LED, the Threshold Pot, or on the Negative Threshold LED.
Termination Switch
In some cases RS-422 and RS-485 pairs are terminated. This termination is usually needed only for long or high speed networks. Terminations usually consist of a 100 ohm one-half watt resistor located at each end of the network. In some complicated multi-drop networks it may be hard to determine exactly were the “ends” are. A 100 ohm one-half watt termination resistor is included in the 485T. It may be helpful if you are testing an existing 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 Out Connector
This is a standard DB-25S RS-232 connector. When the DATA LED is blinking, any RS-422/485 data on the A & B inputs is converted to the RS-232 format and output on pin 2. You can connect this to a device that has an RS-232 port and can read your data. Be sure you turn the threshold pot all the way down (clockwise) to zero. For use on standard ASCII data B&B Electronics sells a program called BreakOut II that will turn a PC into a serial data monitor. With it and a PC you can monitor data on your RS-422/485 network.
NOTE: If your data is garbled you may have the A and B lines connected backwards or the threshold pot may not be all the way down to zero. It is also possible that the RS-422/485 signal may be too weak.
8Documentation Number 485T1995 Manual
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
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