Overview
What are Communication Modules?
Communication modules are specialized hardware interfaces designed to facilitate data exchange between a Programmable Logic Controller (PLC) and other external devices. These modules act as the network gateway for the control system, managing the physical layer and protocol requirements necessary for the PLC to talk to Human Machine Interfaces (HMIs), drives, sensors, and other controllers.
By offloading the networking tasks from the main Central Processing Unit (CPU), these modules ensure that the PLC's core logic execution remains fast and deterministic. They support a wide range of industrial standards, from legacy serial connections like RS-232/485 to high-speed industrial Ethernet protocols such as EtherNet/IP and PROFINET. Whether mounted directly on the backplane or used as distributed I/O heads, communication modules are the backbone of integrated industrial automation.
Main Manufacturers
PALM Parts Solution stocks and distributes communication modules from the industry's leading manufacturers to ensure seamless connectivity across your facility:
- Allen-Bradley: Specializing in EtherNet/IP, ControlNet, and DeviceNet solutions.
- Siemens: Leaders in PROFINET and PROFIBUS technologies.
- Mitsubishi Electric: Experts in CC-Link and MELSECNET architectures.
- Schneider Electric: Providing robust Modbus and CANopen integration.
- ABB & GE Fanuc: Reliable solutions for high-availability power and utility networks.
- Beckhoff & B&R Industrial Automation: Pioneers in EtherCAT and POWERLINK high-speed networking.
- Omron, Delta Electronics, & Lenze: Versatile modules for machine-level control.
- SEW-Eurodrive: Specialized communication for drive-train and motion synchronization.
Typical Applications
Communication modules are utilized in virtually every automated industrial environment to enable:
- Distributed I/O Networking: Connecting a central PLC to remote I/O racks located hundreds of feet away.
- Drive Integration: Transmitting speed, torque, and position commands to Variable Frequency Drives (VFDs) and Servo drives.
- HMI/SCADA Connectivity: Providing the data link between the controller and operator interfaces or plant-wide monitoring systems.
- Inter-PLC Data Sharing: Enabling multiple machines on a production line to synchronize their operations.
- IIoT and Cloud Gateways: Bridging shop-floor data to enterprise-level databases for predictive maintenance and analytics.
Popular Product Families
We maintain an extensive inventory of the industry’s most frequently specified communication families:
- Allen-Bradley/Rockwell: 1756-EN2T (ControlLogix), 1769-ENTR (CompactLogix), and 1747-SN (SLC 500).
- Siemens SIMATIC: CP 343-1 (S7-300), CP 443-1 (S7-400), and integrated CM/CP modules for S7-1200 and S7-1500.
- Mitsubishi MELSEC: QJ71 series for Q-Series PLCs and FX3U-ENET modules for compact controllers.
- Schneider Electric: Lexium and Modicon communication adapters for CANopen and Ethernet.
- Beckhoff: EKxxxx and ELxxxx EtherCAT Couplers and Terminals.
- Omron Sysmac: CJ1W-EIP21 EtherNet/IP units and Serial Communications boards.
Replacement & Compatibility
Replacing a communication module requires more than just physical matching; it requires protocol and firmware alignment. When migrating from legacy systems to modern ones, such as moving from PROFIBUS to PROFINET or DeviceNet to EtherNet/IP, gateway modules are often used to maintain compatibility with existing hardware.
Key Considerations for Replacement:
- Firmware Revisions: Ensure the replacement module firmware is compatible with your current PLC software (e.g., RSLogix 5000 vs. Studio 5000).
- Configuration Files: You may need the original GSD, ESD, or XML files to configure the new module in your network master.
- Port Density: Modern replacements often offer dual ports to support Device Level Ring (DLR) topologies where older single-port modules cannot.
- Hardware Series: Some manufacturers (like Allen-Bradley) have Series A, B, and C versions of the same part number; verify if the newer series is backward compatible with your chassis.
Selection Guide
To ensure you purchase the correct communication module for your system, follow these steps:
- Identify the Host Rack: Determine the specific PLC family (e.g., Siemens S7-300 vs. S7-1500) as the backplane connectors are not interchangeable.
- Define the Protocol: Does the downstream device require Modbus RTU, Modbus TCP, EtherCAT, or a proprietary link?
- Determine Data Requirements: For high-speed motion, choose modules supporting CIP Motion or Isochronous Real-Time (IRT) PROFINET.
- Physical Environment: Select modules with appropriate ratings if they will be exposed to extreme temperatures or high vibration levels (e.g., IP67 rated blocks vs. IP20 rack modules).
- Network Topology: If you require a ring or star topology, ensure the module has the necessary built-in switch ports.
7 products · Lenze
Frequently asked questions
What is the primary function of a communication module in a PLC system?
Communication modules act as the bridge between different automation components, allowing devices to exchange data across industrial networks like EtherNet/IP, PROFINET, or Modbus. While a standard PLC CPU manages logic, a dedicated communication module offloads the processing requirements of networking, enabling the system to connect to HMIs, remote I/O, other PLCs, and SCADA systems without taxing the main processor's cycle time.
Which industrial protocols are most commonly supported by these modules?
Industrial communication modules typically support Ethernet-based protocols (EtherNet/IP, PROFINET, Modbus TCP/IP, EtherCAT), Fieldbus protocols (DeviceNet, PROFIBUS DP, CANopen, ControlNet), and Serial protocols (RS-232, RS-485, Modbus RTU). High-performance systems like the Siemens SIMATIC S7-1500 or Allen-Bradley ControlLogix frequently utilize EtherNet/IP and PROFINET for real-time control and high-speed data transfer across modern factory floors.
How do I select the right communication module for my application?
Selection depends on three primary factors: the host PLC platform, the required network protocol, and the data throughput requirements. You must ensure the module is physically compatible with your rack or backplane (e.g., 1756-series for ControlLogix) and that your software environment (Studio 5000, TIA Portal) supports the specific firmware version of the module. Consider whether you need specialized features like DLR (Device Level Ring) or built-in web servers.
Can communication modules bridge two different network protocols?
Yes, many modern communication modules act as gateways or protocol converters. For example, a ProSoft or specialized Schneider Electric module can bridge a Modbus RTU legacy network into an EtherNet/IP architecture. This allows older machinery to communicate with modern enterprise-level systems without replacing the entire control infrastructure, facilitating phased digital transformation and IIoT integration.
Does a new communication module require software configuration to function?
The hardware is usually hot-swappable if the backplane supports it, but significant software configuration is required. After installation, you must define the module in the hardware configuration of your programming software, assign a unique IP address or Node ID, and map the I/O data tags. In complex networks like PROFIBUS or DeviceNet, you may also need to load specific GSD or EDS files to ensure the master controller recognizes the new device.
What is the difference between standard Ethernet and Industrial Ethernet modules?
Standard Ethernet is non-deterministic and unsuitable for high-speed motion control due to packet collisions. Industrial Ethernet (EtherNet/IP, PROFINET) uses specialized hardware and software layers to ensure deterministic data delivery. Industrial modules are also physically ruggedized with better shielding against EMI/RFI and wider operating temperature ranges compared to commercial-grade networking hardware used in office environments.
What is the difference between a linking device and a bridge module?
Linking modules are used to connect two different network types (e.g., EtherNet/IP to Link DeviceNet), while bridge modules typically extend the same network or provide a physical transition between backplanes. Many engineers use the terms interchangeably, but technically, a bridge maintains the same protocol while a linking device often performs protocol conversion or mapping at the application layer.
How can I tell if my communication module has failed?
Most failures are caused by electrical surges, moisture ingress, or internal component degradation. Signs of failure include intermittent "Network Request Timed Out" errors, physical "Module Fault" LEDs, or the inability of the PLC to see the module on the backplane. Before replacing, inspect the cabling and termination resistors, as physical layer issues often mimic hardware failures in industrial communication systems.
Are newer communication modules backward compatible with older PLCs?
Firmware compatibility is critical. If you replace an older module with a newer hardware revision, you may need to update the PLC's hardware profile or the module's firmware to match the existing project version. Use tools like Rockwell’s ControlFlash or Siemens’ Primary Setup Tool to verify that the firmware on the new unit is compatible with your current CPU and software version.
What is the difference between Master and Slave communication modules?
A "master" (or Scanner/Client) module initiates communication and controls the network timing and data flow, whereas a "slave" (or Adapter/Server) module only responds to requests from the master. In a typical architecture, a central PLC will house a Master module to control remote I/O drops, which in turn contain Slave communication modules to report data back to the main rack.