Instruction manual

107
14.2 General Information
The converter may be plugged directly into the 9-pin serial port of a PC or connected
via a standard 9-pin to 9-pin PC serial cable.
The echo jumper must be in the “off” position and will configure the converter for RS-
485 two-wire (only) mode. Up to 32 receivers can be driven by any one RS-485 driver,
allowing you to put together large systems with many drop points. Termination
resistors are recommended - they should be located at opposite ends of the system
and should be AC-coupled terminations as noted on page 17, figure 2.3 of the
converter manual.
No wire type or maximum run length is listed in the RS-485 standard.
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 “+”. Connect the “A” line from the converter to the (-) terminal on the controller.
Disregard any “A” and “B” labels on the controller and only refer to the “+” or “-”
polarity on the label of the controller. Connect the “B” line of the converter to the (+)
terminal of the controller. See the Contact Identification Table above for the correct
contact terminals on the controller.