ControlByWeb X-600M, User Manual

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X-600M Users Manual Modbus Operation
Section 5: Modbus Operation
The X-600M can be controlled and monitored using Modbus/TCP protocol. This provides a standard
means of using the X-600M with devices and software from other manufacturers. This section is not a
tutorial on Modbus and it is assumed that the reader is already familiar with Modbus. Detailed Modbus
information can be found at http://www.modbus.org.
The X-600M functions as a Modbus slave. Host devices, such as PLCs, open a connection with X-600M
on port 502 (configurable under
Network > Advanced Network > Modbus menu tab) and then send
requests to read or set relay states, read input states, or sensor values. When the X-600M receives a
command, it will perform the desired function and return a response.
Note: I/Os that are configured for access by a Modbus master have no security since the Modbus
protocol does not have any security measures. For this reason, I/Os that need to be accessed using
Modbus should be limited unless the X-600M is installed on an isolated network.
The X-600M has no built-in relays or inputs. As such, the Modbus register assignment varies and
depends on the mix of ControlByWeb devices and expansion modules registered with the X-600M. The
Network > Advanced Network > Modbus menu tab presents a display which shows the current
Modbus register assignments. Only I/Os configured in these three tables will be accessible through
Modbus.
To make I/Os available over Modbus TCP/IP, a mapping must be created. I/Os can be added to the
three tables in order to make them available. For example, to make a temperature sensor available as a
holding register at Modbus address 0010, click on the “
--- ” next to address 0010 in the holding register
table. A drop-down list of I/Os will appear. Select the temperature sensor and click Submit . Now the
Modbus master can access the value of the temperature sensor by reading the holding register at
address 0010. Similarly relays and outputs can be mapped to coils by adding them to the
Coils table,
and digital inputs can be mapped to discrete inputs by adding them to the Discrete Inputs table.
The following sections provide an overview and explanation of Modbus operation.
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