Communication protocols
PROGRAMMING MANUAL
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4.3.3
ModbusRTU
The ModbusRTU protocol provides single point to point communication
between the TJ2-MC64 and a ModbusRTU master. Implementation of
the protocol is provided on serial port 1 for RS232 and port 2 for RS485.
Baud rate and slave address can be set in the BASIC program during serial
port initialisation.
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
command.
SETCOM(19200,8,1,2,2,0) ‘set the RS485 port to normal mode.
Functions
The following Modbus functions are supported:
/i
Code Function name
Action
1
Read Coil Status
Read I/O
2
Read Input Status
Read I/O
3
Read Holding Registers
Read VR variables or TABLE memory in both
integer or IEEE floating point format
5
Force Single Coil
Write I/O
6
Set Single Holding Register
Write to a VR variable or a TABLE location in
both integer or IEEE floating point format
16
Set Multiple Holding Registers
Write to multiple VR variables or TABLE loca-
tions in both integer or IEEE floating point for-
mat
23
Read & Write Multiple Holding
Registers
in both integer or IEEE floating point format
Code Function name
Action
