Implementing Modbus TCP Communication on SIMATIC PCS 7 Box Systems (IPC627D)

Implementing Modbus TCP communication on a SIMATIC PCS 7 Box system (such as IPC627D running WinAC RTX) requires configuring open industrial Ethernet communication blocks using the SIMATIC Modbus/TCP software library. Because the PCS 7 Box utilizes a software controller architecture, communication executes through the integrated PROFINET/Ethernet interfaces or an installed CP 1616 card. A dedicated runtime license key registered to the software controller is mandatory for continuous operation. Final procurement of library packages and runtime licenses must be validated with an authorized Siemens distributor.

PCS 7 Box IPC627D Architecture and Controller Options

The SIMATIC PCS 7 Box IPC627D (6ES7650-4BC11-8XB0) is an industrial PC platform that combines the controller (AS) and operator station (OS) within a compact rugged chassis. The AS tier is powered by the software controller WinAC RTX (or CPU 410-based software equivalent in specialized releases), executing real-time automation logic under a Windows Embedded operating environment.

To interface third-party systems—such as power meters, gas analyzers, PLCs, and building management systems—Modbus TCP is commonly deployed. On the IPC627D, communication can be routed through:
- Integrated PROFINET/Ethernet Ports: The motherboard's onboard Intel Gigabit Ethernet interfaces operating under Open User Communication (TCON, TSEND, TRCV).
- CP 1616 Communications Processor: A PCI/PCIe plug-in card (6GK1161-6AA02) providing integrated 4-port real-time switch functionality for PROFINET IO and Ethernet channels.

Selecting the Appropriate Modbus-TCP Library Package

Unlike standard S7-400 modular controllers utilizing CP 443-1 communication processors (MODBUSCP), software controllers and integrated PROFINET interfaces utilize the SIMATIC Modbus/TCP PN CPU library architecture:

Software Package: The SIMATIC Modbus/TCP PN CPU library provides function blocks (such as MODBUSPN or FB 102 MB_PNCL / FB 108 MB_RECS) designed for controllers with integrated Ethernet interfaces.
Controller Role: The block can be parameterized as a Modbus TCP Client (active connection establishment, reading/writing remote servers) or Modbus TCP Server (passive connection listening on TCP port 502).
Licensing Model: The engineering software and block library can be installed freely for programming. However, each runtime controller executing the Modbus blocks requires a dedicated Runtime License Key.
Registration Process: The license key is generated by Siemens based on the software controller's serial number or system identification and stored in a designated data block (REG_KEY). Without a valid registration key, the block functions in demo mode and logs periodic license warnings (error code W#16#A090).

Step-by-Step Configuration via Integrated PN and Open Communication

To configure Modbus TCP on the PCS 7 Box IPC627D:

HW Config Setup:
- In STEP 7 HW Config, verify the PC Station contains the WinAC RTX software CPU and the network interface (CP 1616 or Integrated Ethernet).
- Ensure the IP address, subnet mask, and default gateway match the third-party network segment.
NetPro Connection Configuration:
- For standard Open Communication (TCON), connections can be configured dynamically via data blocks or statically in NetPro as an Unspecified TCP Connection.
Insert Modbus Blocks in CFC:
- Open a CFC chart in the AS project.
- Insert the MODBUSPN block (or MB_PNCL for client applications) into an appropriate cyclic interrupt OB (e.g., OB35).
Parameterize Communication Parameters:
- Assign connection parameters: Remote IP address, Remote Port (502), and Connection ID.
- Configure data mapping parameters: Define the S7 DB memory range that maps to Modbus Holding Registers (40001+), Input Registers (30001+), or Coils (00001+).
Apply License Key: Transfer the registration key provided on the Siemens License Certificate into the block's REG_KEY parameter.

Modbus-TCP Library Selection and Licensing Matrix

The following table details the Siemens software packages for Modbus TCP communication:

Controller / Interface ArchitectureRequired Software PackageTypical MLFB / Order StructureLicense RequirementPCS 7 Box (WinAC RTX / Integrated PN)SIMATIC Modbus/TCP PN-CPU2XV9450-1MB02 (Single License)1 Runtime License per software CPUModular S7-400 with CP 443-1SIMATIC Modbus/TCP CP2XV9450-1MB00 (Single License)1 Runtime License per CP 443-1Redundant S7-400H with CP 443-1SIMATIC Modbus/TCP CP Redundant2XV9450-1MB11 (Redundant Pair)1 Redundant License per H-pairRedundant S7-410 with Integrated PNSIMATIC Modbus/TCP PN-CPU Redundant6AV6676-6YM10-0AX01 Redundant License per H-pair

Commercial Accuracy Disclaimer: Software order numbers (MLFBs), package structures, and firmware compatibility prerequisites vary across PCS 7 versions and hardware platforms. System integrators must confirm exact software entitlements and licensing requirements against the official Siemens Catalog CA 01 and obtain an authorized Siemens distributor quotation prior to purchasing.

Verification

Verify Modbus TCP communication on the IPC627D:
1. In CFC test mode, verify that the MODBUSPN block indicates CONNECTED = True and ERROR = False.
2. Inspect the block's STATUS output word; verify it cycles normally through operational states (16#0000 or idle ready) and does not display license timeout 16#A090.
3. Use a Modbus TCP diagnostic simulator (such as Modscan or Modbus Poll) to read holding registers from the IPC627D; verify that data in the S7 data block matches the external simulator display in real time.
4. Test wire-break recovery: Disconnect the Ethernet cable for 30 seconds, reconnect, and confirm that the block automatically re-establishes TCP connection and data exchange.

Limitations and Operational Precautions

Essential technical and commercial precautions:
- The CP 1616 card is primarily an isochronous real-time (IRT) PROFINET controller. When used for standard TCP/IP communication alongside PROFINET IO, ensure network bandwidth is properly balanced.
- Without entering the valid Siemens license registration key, the Modbus blocks will stop communicating after the demo evaluation period expires, requiring a CPU restart.
- Always implement watchdog timers (WD_Time) in CFC logic to detect stale third-party data if the remote Modbus slave freezes while keeping the TCP socket open.

Engineer FAQ

Can I use standard APL channel blocks with Modbus TCP data?

Yes. Modbus data is deposited into a global Data Block (DB). You can interconnect variables from this DB directly to standard APL blocks, such as FbAnIn or MonAnL, for processing and alarming.

What port does Modbus TCP utilize?

Modbus TCP communication operates by default on TCP Port 502. Ensure local Windows firewall rules on the IPC627D allow inbound and outbound traffic on Port 502.

Is a hardware dongle required for the Modbus PN-CPU license?

No physical USB dongle is required for PN-CPU libraries. The license is a paper/electronic Certificate of License (CoL) that grants a registration key string derived from the CPU hardware serial number.