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RS-485 to RS-232 converter
EMCP 3 AMP connector
TD A (-)
MODBUS - 3
RD A (-) *
*
MODBUS + 5
TD B (+)
MODBUS Ref 4
RD B (+) COMMON
* - For multipoint network, terminate with 180ohm resistors at ends of network trunk
Figure 27: Possible wiring configuration to an RS-485 to RS-232 converter
Line Termination Both ends of the Modbus lines (or the extreme ends of the trunk, for a multipoint network) should have termination between MODBUS+ and MODBUS-. A 0.5W 150Ω resistor may be adequate. If line polarization (see Software Configuration section below) is implemented, a better choice is a 10 nF capacitor (10V minimum) in series with a 0.25W 120Ω resistor. For more details on setting up a Modbus network over a serial line, please refer to RS-485 specifications or Modbus specifications. See the Software Configuration section below for instructions on enabling line polarization. Software Configuration The SCADA data link may require software configuration. The configuration parameters are accessible on the EMCP 3 control panel via the following menu options: Main Menu ↵ Configure ↵ Setpoints ↵ Network ↵ Data Link - SCADA ↵ Baud rate options are the following: 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600, and 115200 baud. (115200 baud not currently supported.) Parity can be set to None, Even, or Odd parity. The Slave Address the unique address for each slave on the Modbus data link. This address is referenced in the data messages, described in the Data Link Layer section
