Resolving SIMATIC PDM Error 'Connection Request Actively Refused by Target Device or a Network Hop' via CP 343-1

In SIMATIC PCS 7 and Step 7 configurations utilizing SIMATIC PDM (V9.0 / V9.1) to configure intelligent motor management systems (such as SIMOCODE pro V) on PROFIBUS DP routed through an Industrial Ethernet communication processor (CP 343-1), the fatal error 'Update diagnostics: Communication: Connection request actively refused by target device or a network hop!' during 'Upload to PG/PC' or diagnostic polling is caused by incompatible CP 343-1 firmware lacking S7 Routing and DPV1 dataset routing capabilities, unconfigured S7 subnet routing paths in NetPro, or missing dummy slot modules in the hardware configuration. PDM requires transparent acyclic DPV1 dataset routing through the Ethernet CP to the PROFIBUS backplane. Upgrading CP 343-1 firmware to a version supporting S7 routing and compiling cross-project routing tables in NetPro resolves the connection refusal.

Architecture of S7 Routing for SIMATIC PDM Across Ethernet and PROFIBUS

In industrial plants, engineering workstations reside on the Ethernet Terminal or Plant Bus, while intelligent field devices (such as SIMOCODE pro V motor protection relays, SIPART positioners, and radar transmitters) reside on lower-level PROFIBUS DP or PA subnets.

To configure these devices without plugging a physical cable into every motor bucket in the electrical switchgear, SIMATIC PDM relies on S7 Routing. PDM sends acyclic DPV1 read/write requests over Ethernet to the controller's communication processor (CP 343-1 or CP 443-1). The CP routes the packet across the backplane to the CPU's DP master interface, which retransmits the dataset to the target SIMOCODE device.

Root Cause Analysis: Why Connection Requests Are Actively Refused

The error message 'Connection request actively refused by target device or a network hop' indicates that an intermediate device along the communication pathway explicitly rejected the TCP/IP or S7 dataset telegram:

Incompatible CP 343-1 Module: Certain older or entry-level CP 343-1 modules (such as early CP 343-1 Lean 6GK7343-1CX00-0XE0 or firmware prior to V2.0) do NOT support S7 Routing of DPV1 datasets. The module accepts standard PG/PC programming telegrams but actively refuses acyclic field device datasets.
Uncompiled NetPro Routing Tables: S7 Routing requires a plant-wide routing table (SDB 999+). If NetPro was not saved and compiled with 'Save and Compile > Check Cross-Network Consistency', the CP does not know which physical port routes to the PROFIBUS subnet.
Missing PG/PC Assignment: In PDM Process Device Network View, the communication interface must be assigned to the configured PG/PC object connected to the Ethernet subnet.

Hardware and Firmware Compatibility: CP 343-1 Routing Limitations

To support SIMATIC PDM routing to SIMOCODE pro V on an S7-300 station:

CP 343-1 Standard / Advanced: Use CP 343-1 Standard (6GK7343-1EX30-0XE0) or CP 343-1 Advanced (6GK7343-1GX31-0XE0).
CP 343-1 Lean Restrictions: While modern CP 343-1 Lean (6GK7343-1CX10-0XE0 Firmware V2.0+) supports basic S7 routing, older firmware versions drop DPV1 parameter telegrams.
Firmware Upgrade: If running older hardware, flash the CP firmware to the latest available version via SIMATIC Manager.

The 'Empty Modules' Requirement in Remote I/O Hardware Topology

When uploading parameters from remote I/O stations (such as modular ET 200M racks hosting SIMOCODE or HART modules), the PDM manual notes: 'Before uploading to PG/PC from remote I/Os, you need to add a corresponding number of empty modules below the head module in the configuration':

The Slot Geometry Issue: PDM maps field devices based on physical slot indexing. If a multi-slot rack (e.g., Slots 4 through 11) has empty spaces that were not configured in HW Config, PDM's slot offset calculations mismatch the physical backplane, leading to connection refusals.
Insert Reserved Slots: In HW Config, insert 'Empty Slot' or 'Reserved' modules in unpopulated slots to ensure the slot numbering matches physical hardware.

Comparison of SIMOCODE Integration Pathways in SIMATIC PCS 7

The following table compares the communication methods available for engineering SIMOCODE pro V devices in SIMATIC PCS 7:

Integration MethodPhysical Routing PathPDM SupportCommissioning ConvenienceHardware CompatibilityS7 Routing via CP 443-1 / S7-400Ethernet -> CP 443-1 -> S7-400 -> PROFIBUS100% NativeCentralized from Engineering StationFully supported across all CP 443-1S7 Routing via CP 343-1 (S7-300)Ethernet -> CP 343-1 -> S7-300 -> PROFIBUSSupported with V2.0+ CPCentralized from Engineering StationRequires Standard/Adv CP 343-1Direct Local USB CableLaptop USB -> SIMOCODE Front Port100% NativeRequires local physical access at MCCAny SIMOCODE pro V unitDirect PROFIBUS CP 5711Laptop USB -> CP 5711 -> PROFIBUS DP100% NativeRequires physical tap into DP cableBypasses controller and Ethernet

Verification

Verify PDM online communication to SIMOCODE pro V:
1. In SIMATIC Manager Process Device Network View, right-click the SIMOCODE device and select Open Object.
2. SIMATIC PDM opens the parameter window; verify that the bottom status bar displays 'Online: Connected'.
3. Select menu Device > Upload to PG/PC...; verify that parameter tables (motor rating, trip classes, control functions) upload cleanly with a green progress bar.
4. Select Device > Diagnostics > Update Diagnostics; verify that motor current measurements and thermal memory status update without connection refusal errors.

Limitations and Operational Precautions

Never download parameters to a SIMOCODE motor manager while the physical motor is actively spinning in production; downloading alters control functions and can cause unexpected contactor drops. When performing S7 Routing across complex networks, ensure that port 102 (ISO-on-TCP) is open on all intermediate corporate firewalls and that the S7 subnet IDs match across project boundaries in NetPro.

Engineer FAQ

Why does SIMATIC Manager download to the PLC successfully, but PDM fails to connect to SIMOCODE?

SIMATIC Manager downloads program blocks using standard S7 communication to the CPU. PDM requires S7 Routing of DPV1 datasets through the CPU to the subordinate PROFIBUS slave. If the Ethernet CP lacks DPV1 routing capabilities, PDM fails even while standard Step 7 downloads work.

What does 'network hop' mean in the PDM error message?

A 'network hop' refers to a gateway device (such as the CP 343-1 or the CPU backplane) that transitions the communication packet from one subnet (Ethernet) to another (PROFIBUS DP).

Can I use SIMOCODE ES software instead of SIMATIC PDM?

Yes. SIMOCODE ES is the dedicated engineering software for SIMOCODE pro. When integrated into Step 7, it utilizes the same S7 routing infrastructure as SIMATIC PDM.