Motion Coordinator Technical Reference Manual
Communications Protocols 13-3
MODBUS RTU
MODBUS RTU
Introduction
A growing number of programmable keypads and HMIs provide the user with a
choice of serial interface protocols to enable communication with various PLCs
and Industrial Computers. One such protocol is Modbus RTU. The Motion Coordi-
nator system software provides built-in support for the Modbus protocol.
Scope of Operation
This document applies to Motion Coordinators with system software version 1.48
and above.
The Modbus RTU protocol provides single point to point communication between
the Motion Coordinator and a programmable keypad/display. Implementation of
the protocol is provided on serial port 1 for RS232 and port 2 for RS485. Port 0 is
the main programming port and does not have the Modbus option. Baud rate and
slave address can be set in the Trio BASIC program during serial port initialisation.
Initialisation and Set-up
The Modbus protocol is initialised by setting the mode parameter of the SETCOM
instruction to 4. The
ADDRESS parameter must also be set before the Modbus
protocol is activated.
example:
ADDRESS=1
SETCOM(9600,8,1,2,1,4) ‘Port 1 as MODBUS port at 9600 baud
ADDRESS=1
SETCOM(19200,8,1,2,2,4) ‘set up the RS485 port at 19200 baud
The protocol can be de-selected by setting the option to 0 in the SETCOM com-
mand.
SETCOM(19200,8,1,2,2,0) ‘set the RS485 port to normal mode
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