Serial Port; Rs485 Connections - Bitronics M350 User Manual

4.2 Serial Port

This port when ordered can be set to RS-232 or RS-485, and support baud rates up to
115200. Set-up of the Serial Port can be accomplished by using a web browser
connected to the Ethernet port, or via the front display buttons (Setup menu -
Serial). The default configuration for the serial ports is:
Serial Port Default Setting
Port Protocol
Serial DNP 3
Serial cable requirements for RS485 connection:
Tie RS-485 cable shields (pin 15) to earth ground at one point in system.
The recommended torque ratings for the terminal block wire fasteners are listed in the
Physical Specifications table (section 1.3).
Transient Voltage Suppressor (TVS) clamp devices are used on the serial port as the
method of protection. The serial port is clamped to a voltage of 16.7-18.5V nominal,
24.46V max. The clamps are rated for a peak pulse current of 24.6 max.

4.2.1 RS485 Connections

Note that various protocols and services have different port connection requirements.
When making connections to serial ports for Modbus or DNP3 over RS485, 2-wire half
duplex is required. This is because it is imperative to maintain a minimum time period
(3 1/3 characters) from the time the transmitter shuts off to the next message on the
bus in order to guarantee reliable communications. See figure 7 below for RS485
cable wiring diagrams.
ML0038
Parity
None
September 27, 2017
IED
Baud Physical Media
9600 1 RS-232
- 38 -
Copyright 2017 Bitronics, LLC
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