Contrec 515 BR03, Operation Manual

Page: 80 / 110

Communications
70 515 BR03 - 15 August 2021
COM-2 RS-485 Port Option
The COM-2 RS-485 port enables communication with multiple devices.
Each device has a unique address so that the “master” device can
communicate with specific “slave” devices.
On RS-485 links, an external terminating resistor must be connected at the
furthest end of the cable. When multiple instruments are connected, they
should be “daisy chained” in a multidrop configuration as shown in Figure
16. Up to 32 units can be connected to the interface at a maximum distance
of 1200 metres.
Figure 16 RS-485 Connections
COM-2 Ethernet Port Option
An Ethernet module is an available option, in place of the RS-485 port, if
Modbus TCP/IP connection is required. In the programming
communication settings, COM-2 should be set to RTU (Modbus), 19200
Baud rate, even parity and 1 stop bit.
For further advice and example of Ethernet port usage and setup, refer to
Ethernet Port & Setup on page 94 in the Appendix.
Protocols
The communications protocols can be assigned to the communication ports
on the instrument as follows:
•
ASCII - Simple ASCII
•
RTU - Modbus RTU
•
PRN - Printer Protocol
•
NONE - If a port is not being used, set the protocol to NONE.
Note: The Printer Protocol is only available if the option with Real Time
Clock is installed. Also a protocol cannot be assigned to more than
one port at a time as described in
Communications on page 59.
Twisted Pair
Load
120 ohms
Gnd Gnd
Host
Computer
Comms
Gnd
+
-
+ -
+ -
Instrument Instrument
19 20 21
19 20 21