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15. ModBus Transactions
Introduction
ModBus Transactions feature allow exchanging data between two or more ModBus stations via any
communication ports.
One often speaks of 'Master Network' because it is a ModBus Master communication: the Master
(
TB
OX
LT2
) executes reading and writing in slave(s) through any media (RS485, Ethernet, modem...).
The protocol will be ModBus-RTU or ModBus/TCP according to the media used.
Each ModBus Transaction corresponds to one transaction (reading or writing) with 1 slave.
When there are several stations,
TB
OX
LT2
executes the different transactions of one station at a time,
then transactions of the following station, and so on …
When a dial-up modem is used to execute ModBus Transactions,
TB
OX
LT2
needs first to establish the
connection using an Alarm of type ‘ModBus’ (see chapter 12.4. Recipients)
Before creating a ModBus Transaction you have to create the equipment you are going to communicate
with.
15.1. Creating a Remote Device
From the Project Workspace,
select ‘Resources’

‘I/O’. Click
‘I/O’ and in the list of I/O, click
‘Add an I/O Card’.
Select ModBus Device.
Name: You type any name. It will be
available in a list of available
equipment when creating ‘ModBus
Transactions’ (see next).
Address: It is the station address of the Remote
equipment. It must be different from
the
TB
OX
LT2 and possible other
equipment on the same network.
When communicating through
TCP/IP port, you have to indicate the
IP address of the remote device
RTU Port: The communication port used by
TB
OX
LT2 to communicate with the
remote equipment.