S7-1200 PLC
Communication
The S7-1200 PLC is a compact controller launched by Siemens, supporting various communication protocols and interfaces, suitable for device interconnection in industrial automation scenarios.
1. Supported Communication Protocols and Interfaces
1. Integrated Interfaces
PROFINET (default support)
Supports real-time communication (RT) and isochronous mode (IRT), used to connect HMI, drives, remote I/O, and other devices.
Maximum number of nodes: up to 16 connections (client/ server).
Supports open communication (OUC), implemented through TSEND_C/TRCV_C function blocks for TCP/UDP communication.
2. Expansion Communication Modules
RS485/RS232 Module (CM1241)
Supports Modbus RTU (master/ slave), USS protocol (Siemens inverter communication).
PROFIBUS DP Module (CM12435)
Supports PROFIBUS DP slave communication.
Ethernet Module (CP12431)
Supports MQTT, HTTPS, TCP/IP and other protocols, suitable for cloud communication or remote monitoring.
3. Communication Board (CB1241)
Provides additional RS485 interface for expanding Modbus RTU or USS communication.
2. Communication Configuration Steps (using TIA Portal as an example)
1. Hardware Configuration
Add S7-1200 PLC and communication modules (such as CM1241).
Configure communication interface parameters (such as baud rate, parity, station address, etc.).
2. Protocol Configuration
PROFINET
Assign device name, set IP address (e.g., 192.168.0.1).
Modbus RTU
Use `MODBUS_COMM_LOAD` to initialize the communication module.
Call `MB_MASTER` or `MB_SLAVE` function blocks to implement master/ slave communication.
TCP/UDP
Use `TSEND_C` (connection-oriented send) and `TRCV_C` (connection-oriented receive) function blocks.
3. Typical Application Scenarios
1. Communication with HMI
Connect to Siemens touch screens (such as KTP700) via PROFINET or Ethernet, using HMI variables directly mapped to PLC data blocks.
2. PLC Inter-communication
S7 Communication: Exchange data with S71500 or S71200 using PUT/GET instructions.
TCP Communication: Transfer data between devices across networks (requires configuration of TSEND/TRCV).
3. Inverter Control
Use USS protocol to control Siemens G120 inverter via RS485, setting frequency or reading status.
4. Cloud Platform Connection
Upload data to MindSphere or Alibaba Cloud via CP12431 module (requires configuration of MQTT/HTTPS).
4. Common Issues and Troubleshooting
1. Communication Interruption
Check physical connections (network cables, terminal resistors).
Ensure IP address/ subnet mask configurations are consistent.
Use TIA Portal online diagnostic function to check module status.
2. Modbus RTU Data Errors
Confirm baud rate, data bits, stop bits match with the slave.
Check register address offsets (e.g., Modbus address 40001 corresponds to PLC address 0).
3. PROFINET Device Not Connected
Assign device name in hardware configuration and use “AssignDeviceName” tool to update.
5. Precautions
Firmware Version: Ensure PLC and communication module firmware versions are compatible (e.g., V4.0 and above support OUC).
Real-time Performance: PROFINET IRT requires use with switches that support IRT.
Resource Limitations: S71200 communication connection count is limited by CPU model (e.g., CPU1214C supports a maximum of 8 TCP connections).
Through flexible configuration, S71200 can achieve seamless integration with various industrial devices, meeting the communication needs of small to medium-sized automation systems.
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