B&B Electronics 485COSR1 - Datasheet - Manual (Page 2)

Document No. 485COSR10812 - pg. 2/2
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No wire type or maximum run length is listed in the RS-485 Standard. However, the RS-422 Standard, which is
very similar, recommends number 24 AWG twisted-pair telephone cable with a shunt capacitance of 16 picofarad per
foot and no more than 4000 ft. of distance.
The polarity of the two RS-485 lines must be correct. With no data being sent, the RS-232 line should be
negative and the RS-485 "A" terminal should be negative with respect to the "B" terminal. If your equipment uses a "+"
and "-" naming scheme, in most cases the "A" line will be connected to the "-" and the "B" line will be connected to the
"+".