Siemens Implementation

Modbus TCP/IP for Siemens

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

S7-1200/1500 have integrated PN/IE ports with native Modbus TCP. Uses MB_CLIENT/MB_SERVER with TCON connection management. No special hardware required beyond Ethernet.

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.

Siemens Hardware Requirements

Compatible Communication Modules

Integrated PN/IE port (all S7-1200/1500 CPUs)

CP 343-1 (S7-300 Ethernet)

CP 443-1 (S7-400)

CP 1543-1 (S7-1500 advanced)

SCALANCE X switches

Wiring Details

Network Setup

Standard TCP/IP on port 502. Configure IP via Device Configuration. Cat5e/Cat6 cable, 100m max per segment.

Siemens Software & Programming

Function Blocks & Instructions

MB_CLIENT (Modbus TCP client)

MB_SERVER (Modbus TCP server)

TCON (connection establishment)

TDISCON (disconnect)

TSEND/TRCV (low-level TCP)

Siemens Code Example

TCON(REQ := TRUE, ID := 1, CONNECT := ConnectionDB);
MB_CLIENT(
  REQ := TriggerRead,
  MB_MODE := 0,
  MB_DATA_ADDR := 40001,
  MB_DATA_LEN := 10,
  MB_DATA_PTR := DataBuffer,
  CONNECT := ConnectionDB,
  => DONE => ReadDone,
  => STATUS => StatusWord
);

Siemens-Specific Implementation Notes

Automatic connection management with TCON/TDISCON. S7-1500 supports 64 simultaneous connections. STATUS 80C4H = connection error, 80A1H = parameter error. Typical response time 5-20ms on 100Mbps network.

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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