This architecture uses a Siemens S7-1200 as the Modbus TCP master to exchange data with a Zelio controller fitted with an Ethernet Modbus module. A KTP 400 operator panel provides the operator interface. The available evidence confirms a narrow data exchange: eight word registers in total, divided into four for writing and four for reading.
Communication Architecture
Connect the S7-1200 and the Ethernet-equipped Zelio through the available Ethernet network, then configure the PLC as the Modbus TCP master. The source does not provide IP addresses, port settings, register addresses, command identifiers, or software versions; obtain these values from the actual device configuration and project before implementing the connection.
Register Capacity and Direction
| Data function | Supported capacity | Implementation constraint |
|---|---|---|
| Write | 4 word registers | Map only the commands or setpoints that the application requires. |
| Read | 4 word registers | Map only the essential states or process values. |
| Total exchange | 8 word registers | Do not design the interface around additional words without verifying device support. |
The evidence does not define whether “read” and “write” are stated from the S7-1200 or Zelio perspective. Confirm the direction against the Zelio data map before assigning PLC tags or HMI objects.
Configuration Procedure
- Place the S7-1200, KTP 400, and Zelio Ethernet module on the intended Ethernet network.
- Configure the S7-1200 as the Modbus TCP master.
- Map no more than four words for writes and four words for reads, using the register addresses documented for the installed Zelio module.
- Bind the required KTP 400 controls and indicators to the corresponding PLC data.
Keep the application small enough to fit the confirmed register limit. The architecture is suited to simple automation or home-automation functions where an existing Ethernet network is available.
Commissioning Verification
Test each mapped word independently. Change one command value from the operator interface and confirm that the intended destination value changes; then change one Zelio status value and confirm that it reaches the PLC and appears correctly on the KTP 400. If data moves in the wrong direction, revisit the read/write perspective and register mapping rather than adding unverified addresses.
FAQ
How many registers can the S7-1200 exchange with Zelio?
The stated limit is eight word registers: four for writing and four for reading.
Which device acts as the Modbus TCP master?
The Siemens S7-1200 acts as the Modbus TCP master, while the Zelio uses an Ethernet Modbus module.
How do I verify the S7-1200-to-Zelio register mapping?
Exercise each mapped word separately and confirm the value at both endpoints and on the KTP 400. Verify the documented direction because the evidence does not define whose perspective determines “read” and “write.”