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ML0042 October 15, 2019 Copyright 2019 Bitronics, LLC
The M66x has an optional serial port that is user configurable for RS232 or RS485,
and support baud rates up to 115200. See section 4.4 for screen shot showing web
configuration for serial port. For meters with a display, the serial port can also be
setup via the front display buttons (Setup menu -
1.4
Serial).The RS-232 drivers
support full and half duplex modes. The default configuration for the serial ports is:
Serial Port Default Settin
Port Protocol Parit
Baud
IED
Ph
sical Media
Serial DNP 3 None 9600 1 RS-232
Serial cable requirements for RS485 connection:
Tie RS-485 cable shields (pin 18) to earth ground at one point in system.
The recommended torque rating for the terminal block wire fasteners are listed in the
Physical Specifications table (section 1.3).
A Transient Voltage Suppressor (TVS) clamp device is used on the serial port as the
method of protection.
3.5.1 RS232/485 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. However, when using
ZMODEM or connecting to the remote display, asynchronous 2-way communications
are required, and therefore a 4-wire full duplex (technically RS422) connection is
needed. See figure 5 below for RS485 cable wiring diagrams showing 2 wire and
figure 6 for RS232 wiring.
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