4-1
IM 04L51B01-01EN
Using Modbus Functions (Communicating with Modbus devices)
4
4.1 UsingModbus/TCPtoEnableOtherDevicesto
Read Data from and Write Data to the GX/GP
(Modbusserverfunction)
The Modbus function is used by the GX/GP and external Modbus devices to perform
communication and data reading and writing.
The GX/GP can operate as a Modbus server. The maximum number of simultaneous
connections is 4.
Other devices (Modbus client devices) can carry out the following operations on the GX/GP.
• Read I/O channel and math channel (/MT option) data
• Read communication channel (/MC option) data
• Write data to communication channels
• Start and stop recording, write messages, and perform other operations
• Load the recording start/stop condition, message strings, and other types of data
Modbus client device
GX/GP
Modbus server
Ethernet
Command
Input register
Hold register
Read
Write
Read
3XXXXX
4XXXXX
Write
Read
Read
GX/GP internal register
Client
4.1.1 SettingBasicNetworkCommunicationConditions
Description
• ObtaintheIPaddressautomatically
• SettheIPaddressmanually(whenautomaticIPaddressassignmentisset
toOff)
For details on the settings, see page 1-143 in section 1.17.1, “Setting Basic Communication
Conditions”.
4.1.2 Configuring the Modbus Server Function
Description
EnablingtheModbusServerFunction
For details on the settings, see page 1-157 in section 1.17.9, “Setting the Server Functions
to Use (FTP, HTTP, SNTP, MODBUS, GENE, DARWIN compatible communication)”.
Applying Modbus Connection Limits
Set this function to limit the IP addresses that can connect to the GX/GP Modbus server
function.
You can register up to 10 IP addresses.
For details on the settings, see page 1-156 in section 1.17.8, “Limiting the Connection to
the Modbus Server (GX/GP)”.
Chapter 4 UsingModbusFunctions(CommunicatingwithModbusdevices)
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