1. Core Communication Protocols: The Engineer’s Toolbox
We categorize the most commonly used communication methods into three main types to facilitate quick selection in your projects.
First Type: The most integrated and mainstream “one-stop” solution
1. PROFINET (Key Focus)
This is the absolute mainstream and preferred choice for Siemens S7-1200/1500/400 series, representing the implementation of industrial Ethernet.
Engineering Application Scenarios:
Controller and IO Devices: Connecting the CPU with distributed IO stations (such as ET200SP, ET200MP). This is the core application.
Controller and Drives: Connecting servo/inverter drives like V90/G120/S210 for periodic data exchange (PLC->Drive: Control word/Setpoint; Drive->PLC: Status word/Actual value).
Inter-controller Communication: Multiple PLCs exchanging data via S7 communication or open TCP/IP communication.
HMI Connection: The default connection method between touch screens and PLCs.
Technical Points:
RT: Real-time communication for IO data refresh, ensuring jitter <1ms, meeting most automation needs.
IRT: Isochronous real-time for motion control and other high-precision synchronization applications, jitter <1μs. Network topology must be planned during configuration.
Device Naming: PROFINET uses device names for addressing instead of IP addresses. This is the most common mistake for beginners! The device name assigned in hardware configuration must match exactly with the name assigned by the PLC/PG for the device to start and exchange data.
Topology Recognition: Automatically identifies network structure, facilitating diagnosis and maintenance.
Operations in TIA Portal:
Drag and drop devices from the hardware catalog into the network view.
Right-click on the device and select “Assign Device Name”.
Configure the address of IO modules and use these I/O addresses directly in the program.
Second Type: Classic and stable fieldbus still widely used
2. PROFIBUS-DP
Although the trend is towards PROFINET, existing projects and some new projects (especially in low-cost or harsh environments) still use it extensively.
Engineering Application Scenarios:
Connecting traditional distributed IO (such as ET200M, ET200S).
Connecting drives, valve islands, and other field devices that do not support PROFINET.
Technical Points:
Master-slave structure: A network has only one master (usually the PLC) and multiple slaves.
Diagnostics: Strong diagnostic capabilities can diagnose faults down to the module level.
Addressing and Speed:
Address: Each slave has a unique station address (0-126).
Speed: Ranges from 9.6Kbps to 12Mbps, must be uniformly set during configuration, and all devices must support the selected speed.
GSD File: When adding third-party PROFIBUS devices, their GSD file must be installed for TIA Portal to recognize and configure it.
Operations in TIA Portal:
Add a PROFIBUS master module and PROFIBUS network in the network view.
Drag and drop slaves from the hardware catalog or installed GSD files onto the PROFIBUS network.
Set station addresses and communication speeds for each slave.
Third Type: Open protocols for system integration and cross-brand interconnectivity
3. OPC UA
This is the best choice for achieving IT and OT integration and communication with upper-level systems.
Engineering Application Scenarios:
SCADA/MES/ERP systems collecting production data from PLCs.
Uploading device data to cloud platforms.
Data exchange between controllers of different brands (as long as both support OPC UA).
Technical Points:
Client/server model: PLC acts as a server, while upper-level systems act as clients to access data.
Information Modeling: Provides not only data values but also the type, structure, and meaning of the data, making it “readable”.
Security: Built-in user authentication, encryption, and authorization mechanisms, making it very secure.
Platform Independence: Does not rely on Windows; PLCs like S7-1500 can natively embed OPC UA servers.
Operations in TIA Portal:
Activate the “OPC UA Server” function in the CPU properties.
Define the variables to be exposed and organize them into different “namespaces”.
Configure security policies and user permissions.
4. Open User Communication
Used when communication with non-Siemens devices (such as robots, vision systems, third-party instruments, custom upper-level software) is required.
Protocols: TCP/IP, ISO-on-TCP, UDP.
Engineering Application Scenarios:
Communicating with AGV controller via Ethernet.
Socket communication with upper-level software written in Python/C#.
Connecting smart instruments that support Ethernet communication.
Technical Points:
Requires programming implementation. Use instruction blocks like TSEND_C, TRCV_C, TCON, TDISCON in TIA Portal.
Must clearly define both parties’ IP addresses, port numbers, and data frame formats (who sends first, length of transmission, byte order, etc.).
ISO-on-TCP is more suitable for industrial environments than regular TCP, as it ensures the integrity of data packets.
2. Engineer’s Communication Selection Guide
Scenario Preferred Protocol Key Reasons and Considerations
New project planning, connecting IO/drives PROFINET Future trend, optimal performance, comprehensive functionality, one-stop solution.
Maintaining or upgrading old production lines PROFIBUS-DP Compatible with existing devices, stable and reliable, potentially lower costs.
Siemens HMI connecting Siemens PLC S7 Protocol (based on PN/PB) High integration, simplest configuration, no programming required, stable performance.
Interacting with MES/ERP/cloud platforms OPC UA Open standard, secure, cross-platform, strong information modeling capabilities.
Connecting third-party devices (non-Siemens) Open TCP/IP Most versatile, almost all devices with Ethernet ports support it.
Data exchange between multiple Siemens PLCs S7 Communication (based on PN/PB) Simple configuration, high efficiency, superior to open communication.
Connecting third-party PROFIBUS devices PROFIBUS-DP + GSD file Must obtain and install GSD file from the supplier.
3. Practical Process and Core Concepts
Hardware Configuration: Build a real hardware structure in TIA Portal, which is the foundation of all communication.
Network Planning: In the network view, use the mouse to drag and connect lines to establish physical connections.
Parameter Configuration:
PROFINET: Set IP address, subnet mask, and ensure device names are assigned.
PROFIBUS: Set station addresses and communication baud rates.
S7 Connection: Specify the rack number and slot number of the communication partner.
Open Communication: Specify IP address and port number.
Programming/Data Mapping:
PROFINET/PROFIBUS IO: Use the I/Q addresses assigned in hardware configuration directly.
S7 Communication: Use PUT/GET instructions or configure unidirectional connections, using mapped DB block addresses.
Open Communication: Call instruction blocks like TSEND_C/TRCV_C for programming.
Download and Diagnostics:
Download configuration and programs to the PLC.
Use TIA Portal’s online and diagnostic features, topology view, online backup, etc., for powerful network diagnostics, quickly locating issues like disconnections, address errors, and device mismatches.
Summary
As automation engineers, we should have these “wrenches” in our toolbox:
PROFINET: Your main electric wrench, handling most heavy and precise tasks.
PROFIBUS: Your classic manual wrench, reliable and durable, adept at handling old issues.
S7 Protocol: Your specialized socket, most efficient when dealing with in-house (Siemens) devices.
OPC UA: Your universal adapter, responsible for connecting to the “outside world” (IT systems/cloud/other brands).
Open TCP: Your general toolset, always able to solve problems when no specialized tools are available.