
EliteIQ
TM
User Manual
44
9M02-7100-A001-EN
Version B
6
Modbus RTU Master
6.1 Overview
The Modbus Master Interface enables the EliteIQ to read input values from a Modbus sensor, PLC or Modbus
Slave device and write relay control values to a Modbus sensor, PLC or Modbus Slave device. The connection
uses the RS-232 serial connector on the EliteIQ. The protocol is Modbus RTU, where the EliteIQ is the Master
and the Modbus sensors, PLC or Modbus I/O is the Slave.
The option supports a combination of up to 72 total I/O channels – up to 48 of which can be physical I/O in the
EliteIQ.
The I/O in the Modbus Slave can be any combination of analog (holding registers) or digital points (coils).
Values that are read from the Modbus Slave are interpreted by the EliteIQ the same as if they were physical I/O in
the EliteIQ. All the alarm and control logic within the EliteIQ operate on data coming from Modbus registers.
The communications link between the EliteIQ and the Modbus slave devices is monitored several times a second.
If the communications link stops functioning after repeated attempts, a Communications Channel (06) alarm is
initiated. This alarm is treated exactly like any other system alarm, allowing the system to call out, drive local relay
or issue reports.
Port 2 or Port 3 can be used as a RS-232 connection (DB9) or as a RS-485 connection (5-position plug). RS-232
Port 2 is J-11, RS-232 Port 3 is J-9 and both RS-485 ports are on J-17.
The RS-232 port is configured as a DTE device, as follows:
Pin 2
RCV
Pin 3
XMT
Pin 5
GND
6.2 Initializing the Modbus Master Interface
The Modbus Master Interface is setup by defining the following:
•
Serial port 2 or 3 can be selected as a Modbus Master – default baud rate is 38400
o
You can also set the Max Idle, Max Timeout and RS-232 or RS-485 mode
•
EliteIQ I/O slots can be identified as Modbus I/O – default is that no slots are enabled as Modbus I/O slots
There are eight Modbus I/O channels per Slot. You can enable as many slots as you have purchased. For
example, if you purchased a 32-channel Modbus Master configuration, then you can enable any four slots which
do not have physical I/O cards attached.
All of these can be defined through the integral keypad.