Beckhoff Implementation

Modbus TCP/IP for Beckhoff

Ethernet-based variant of Modbus using TCP/IP. Combines simplicity of Modbus with speed and scalability of Ethernet.

Type: Industrial EthernetSpeed: 10/100/1000 MbpsReleased: 1999Organization: Modbus Organization

1 Gbps capable

Bandwidth

Unlimited (network dependent)

Max Nodes

100m per segment (with switches: unlimited)

Max Distance

Real-Time

Protocol Overview

Beckhoff TwinCAT 3 uses Tc2_ModbusTCP library for both master and slave. Runs on Windows embedded PC, leverages standard Windows TCP/IP stack for Modbus TCP communication.

When to Use Modbus TCP/IP

Choose Modbus TCP/IP for SCADA systems, plant-wide networks, remote monitoring, or when integrating industrial equipment with IT systems.

Beckhoff Hardware Requirements

Compatible Communication Modules

CX Series embedded PC (built-in Ethernet)

C6015/C6025 ultra-compact IPC

Any TwinCAT3-compatible PC with Ethernet

Wiring Details

Network Setup

Standard Windows networking. Configure IP in Windows Network Settings. Port 502 for Modbus TCP.

Beckhoff Software & Programming

Function Blocks & Instructions

FB_MBTCPClient (Tc2_ModbusTCP)

FB_MBTCPServer

FB_ClientServerConnection

FB_MBReadHoldingRegs

FB_MBWriteHoldingRegs

Beckhoff Code Example

fbModbusTCPClient(
  sIPAddr := '192.168.1.10',
  nTCPPort := 502,
  nUnitID := 1,
  nQuantity := 10,
  nMBAddr := 0,
  cbLength := SIZEOF(arrData),
  pDestAddr := ADR(arrData),
  bExecute := TRUE,
  => bBusy => bBusy,
  => bError => bError
);

Beckhoff-Specific Implementation Notes

Leverages Windows TCP/IP stack. Supports TLS/SSL for secure Modbus TCP. Error ID provides detailed Windows socket errors. Typical response time <5ms on Gigabit. Can handle 100+ simultaneous connections limited only by PC resources.

Technical Specifications

Physical Layer

Physical Layer: IEEE 802.3 Ethernet
Cable Type: Cat5e/Cat6 Ethernet
Topology: Star, Tree, Ring
Power Over Cable: No

Data Layer

Data Link: TCP/IP
Encoding: Binary
Error Detection: TCP checksum
Frame Size: 1500 bytes (MTU)

Performance

Scan Time: 1-10ms typical
Deterministic: No
Real-Time: No

Certification

Certification Required: No
License Cost: Free (open standard)
Version: Current

Advantages & Disadvantages

Advantages

✓High speed (up to 1 Gbps)
✓Uses standard Ethernet infrastructure
✓Unlimited nodes and distance (with switches)
✓Easy IT integration
✓Simple protocol (Modbus heritage)
✓Open standard and free
✓Remote access capability

Disadvantages

✗Not deterministic (not real-time)
✗No built-in security (requires VPN/firewall)
✗Higher latency than dedicated fieldbuses
✗Requires managed switches for large networks
✗No device profiles or configuration tools

Common Use Cases & Applications

SCADA systems

Plant-wide data collection

Building management systems

Remote monitoring

Enterprise system integration

Large distributed systems

Industry Adoption

Adoption LevelVery High

Market Share25-35% of industrial Ethernet

Geographic PresenceWorldwide

Primary Industries

Oil & GasWater/WastewaterBuilding AutomationManufacturingEnergy

Supported Message Types

Read Coils

Read Discrete Inputs

Read Holding Registers

Write Single Coil

Write Single Register

Write Multiple Registers

Supported PLC Brands

Siemens Allen-Bradley Mitsubishi Schneider Electric Beckhoff ABB Rockwell

Phoenix Contact

Wago

Protocol Comparisons

Modbus TCP/IP vs EtherNet/IP

Modbus TCP is simpler and open; EtherNet/IP offers better diagnostics and CIP ecosystem

View Detailed Comparison →

Quick Links

Alternative Protocols

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