Communication is a key part of modern industrial automation. PLCs rarely work alone—they constantly exchange data with HMIs, SCADA systems, drives, remote I/O stations, energy meters, sensors, and other PLCs.
This infographic explains the most important communication blocks used in Siemens TIA Portal and shows how they are applied in real industrial projects.
MB_COMM_LOAD
Used to load and initialize Modbus communication parameters before Modbus communication begins.
Always configure MB_COMM_LOAD before using Modbus communication blocks.
MB_MASTER
Allows the PLC to act as a Modbus Master.
The PLC sends requests and reads or writes data from Modbus Slave devices such as:
HMIs
VFDs
Energy Meters
Sensors
Remote I/O
MB_SLAVE
Allows the PLC to operate as a Modbus Slave device.
The PLC responds to requests coming from a Modbus Master.
Common applications include communication with:
SCADA Systems
HMIs
Other PLCs
MB_CLIENT
Used for Modbus TCP communication over Ethernet.
The PLC acts as a Modbus TCP Client and exchanges data with Modbus TCP Servers.
Applications:
SCADA Integration
Gateways
Third-Party Devices
Remote Systems
PUT / GET
Used for S7 communication between Siemens PLCs.
PUT = Write data to another PLC
GET = Read data from another PLC
One of the simplest methods for exchanging data between Siemens controllers.
TSEND / TRCV
Used for open TCP communication.
TSEND = Send data
TRCV = Receive data
These blocks are commonly used for communication with:
PCs
SCADA Systems
Databases
IoT Platforms
Third-Party Devices
TCON / TDISCON
Used to establish and disconnect TCP communication connections.
TCON = Open Connection
TDISCON = Close Connection
These blocks are often used together with TSEND and TRCV.
Communication Examples
This infographic demonstrates how communication blocks work together in real industrial applications:
PLC 
VFD
PLC HMI
PLC SCADA
PLC Energy Meter
PLC Remote I/O
PLC PLC
PLC Cloud Systems
Typical Applications
Modbus RTU Networks
Modbus TCP Networks
Siemens PLC-to-PLC Communication
Machine-to-Machine Communication
SCADA Integration
Industrial IoT Solutions
Energy Monitoring Systems
Plant-Wide Data Collection
Important Rule
Choose the communication block based on the protocol you are using:
• Modbus RTU → MB_COMM_LOAD + MB_MASTER / MB_SLAVE
• Modbus TCP → MB_CLIENT
• Siemens PLC to PLC → PUT / GET
• Open TCP Communication → TCON + TSEND/TRCV + TDISCON
Mastering these communication blocks will allow you to connect PLCs with almost any industrial device and build powerful automation systems.
