Configuring ProTool Communication with S7-300 via CP342-5

Problem Overview: ProTool Cannot Establish Profibus DP Link to S7-300

A classic configuration problem appears when an operator panel running Siemens ProTool (or ProTool/Pro RT) must communicate with an S7-300 station that exposes its automation data through a CP 342-5 DP communications processor on the backplane rather than through the integrated MPI/DP port of the CPU. The typical symptom is one of the following:

• The OP connects to the CPU on MPI without errors, but the same OP configured against the CP 342-5 returns "connection not established" or "station failure".
• Communication is initially possible on Profibus DP, but the OP loses the link as soon as a second device (PG, drive, or another OP) is added to the bus.
• A previously working WinCC application is replaced with a ProTool project, and the new project fails to establish any Profibus DP association even though the bus wiring, terminating resistors, and CP firmware are unchanged.

The reference case discussed in this article involves a CPU 314 occupying slots 2 and 3 of the S7-300 rack, MPI address 2, and a CP 342-5 DP (order number 6GK7 342-5DA02-0XE0 or comparable) installed in slot 4 with Profibus DP address 8. ProTool is configured with two parallel connections: address 2 / rack 0 / slot 0 for MPI and address 8 / rack 0 / slot 4 for Profibus DP. MPI works; Profibus DP does not.

Root Cause Analysis: Five Independent Failure Paths

Before changing parameters, work through each of the five independent failure paths. They frequently appear together.

Path 1 - Slot Numbering Convention Used by ProTool

ProTool does not always number the S7-300 slots the same way the STEP 7 Hardware Configuration does. In some Siemens HMI communication manuals (especially the older Communication for Windows-based Systems manual that accompanied ProTool V6.x), the slot index in the HMI connection editor counts the CPU as slot 0 regardless of the physical slot it occupies on the rack. With this convention, the CP 342-5 physically installed in slot 4 must be addressed as slot 2 in the ProTool connection (because the CPU occupies slots 0 and 1 in that numbering). The CP 342-5 occupies slot 2 of the logical rack once the CPU has consumed slots 0 and 1.

Verify the convention by:

1. Opening the STEP 7 Hardware Configuration for the S7-300 station.
2. Reading the slot number STEP 7 assigns to the CP 342-5 (typically 4 when the CPU is in slot 2).
3. Cross-checking with the Siemens HMI manual that ships with the ProTool installation CD - if the example uses slot = CPU physical slot, use that; if the example uses logical slot 0 = CPU, subtract the CPU offset.

Path 2 - CP 342-5 Operating Mode (DP Master vs DP Slave)

The CP 342-5 can run as a DP master, a DP slave, or both simultaneously only on the S7-300 master CPU side via its "DP master / DP slave" firmware variant. For ProTool to exchange process data over Profibus DP with the HMI as a passive subscriber, the CP 342-5 must be configured as a DP master in HW Config and the HMI panel must be inserted as a passive DP slave in the same Profibus subnet.

Configuration path:

1. Open HW Config and double-click the CP 342-5 in slot 4.
2. Select Operating Mode tab and tick DP master.
3. Save and recompile (Station > Save and Compile).
4. Download HW Config to the S7-300 station.

Path 3 - Communication Resources on the S7-300 CPU

Each S7-300 CPU has a finite pool of communication resources for online services (PG, OP, S7 communication, S7 routing, HMI). The CPU 314 reserves one resource per active connection. When the OP is moved from MPI to Profibus DP, the resource demand pattern changes because the CP 342-5 now consumes CP-internal resources in addition to CPU resources.

Open HW Config > CPU Properties > Communication tab and verify that the OP connection is granted a resource. For an S7-300 with one MPI/DP port and a CP 342-5, allocate at least 2 resources: one for the PG on MPI and one for the OP through the CP.

Path 4 - CP 342-5 Function Block Wiring (FC1/FC2/FC3/FC4)

Data exchange between the CPU 314 and the CP 342-5 DP is handled by the four standard function blocks shipped with STEP 7:

• FC1 "DP_SEND" - transfers process output data from CPU to CP 342-5 (input image).
• FC2 "DP_RECV" - transfers process input data from CP 342-5 to CPU.
• FC3 "DP_DIAG" - reads diagnostic data from the CP.
• FC4 "DP_CTRL" - controls CP operating state and modes (deprecated in newer firmware but still present in legacy projects).

These blocks live in the STEP 7 Standard Library under CP 342-5 / CP 343-5. They must be called cyclically in OB1 (or in a watchdog OB if data exchange is safety-critical). If the blocks are missing from the S7 program, ProTool cannot reach the CPU through the CP, even though the CP itself is online.

Path 5 - Migrated WinCC Configuration Leftovers

When an existing WinCC PC project is decommissioned and replaced with ProTool on an OP, the bus configuration often changes from "CP 5611 as master" to "CP 342-5 as master". Two recurring leftovers block ProTool:

• PROFIBUS bus parameters (Tslot, Tset, Ttr, min TSDR, max TSDR) in the WinCC-side PG/PC interface were tuned for a 1.5 Mbps line. Reset to Auto in the OP's interface selection so the OP follows the master's baud rate.
• Highest station address (HSA) on the CP 342-5 may be set lower than the OP's configured address, causing the master to stop polling beyond the HSA. Re-open HW Config, open the CP 342-5 Properties > Profibus, and confirm HSA >= max configured Profibus address on the segment.

Hardware Identification and Order Numbers

STEP-by-STEP Configuration Procedure

Step 1 - Verify the S7-300 Hardware Layout in HW Config

1. Open SIMATIC Manager and double-click the S7-300 station icon to launch HW Config.
2. Confirm the rack assembly: PS 300 in slot 1, CPU 314 in slot 2, I/O slots as required, CP 342-5 in slot 4.
3. Note the Profibus address of the CP 342-5 (default = 8 in the reference case).
4. Save and download to the CPU.

Step 2 - Enable DP Master on the CP 342-5

1. In HW Config, double-click the CP 342-5.
2. Select the Operating Mode tab.
3. Tick the DP master checkbox and confirm the master Profibus subnet is attached.
4. If the HMI must be visible in the bus topology, also enable DP slave only if the HMI exchanges data with a higher-level master; otherwise leave unchecked.
5. Click OK, save HW Config, and download to the CP.

Step 3 - Insert the OP as a DP Slave

1. Right-click the Profibus subnet and select Add DP Slave.
2. Browse the GSD file path of the OP. For an OP/TP, the GSD file is named after the order number (e.g. SIEM8100.GSD or panel-specific).
3. Insert the OP at the next free Profibus address on the bus.
4. Map at least one input word and one output word for acyclic S7 communication or use the OP's default area pointers (clock, date/time, bit-triggered, alarm-triggered, trend request, trend transfer).

Step 4 - Configure the Connection in ProTool

1. Open ProTool CS and load the panel project.
2. Open System > Connections or Communication dialog.
3. Add a new connection: SIMATIC S7 - Profibus.
4. Set the parameters as in the table below.

Step 5 - Resolve the Slot Offset

If the HMI manual example explicitly uses slot = CPU physical slot number, leave the CP slot at 4. If the manual example indicates CPU = logical slot 0, set the CP slot to 2 (CPU occupies 0 and 1). The deciding rule is found in the Siemens TIA Portal Profibus DP configuration documentation for S7-300/400/1500 and the older ProTool Communication Manual.

Step 6 - Transfer the Project to the Panel

1. Compile the ProTool project and start ProSave.
2. Select Transfer > HMI > OP, choose the Profibus interface on the PG/PC, and select the OP's address (typically 8 in the reference case).
3. Initiate the transfer. The OP restarts and loads the new connection parameters.

Diagnostic Buffer and Status Inspection

Before declaring victory, read the CP 342-5 diagnostic buffer and the CPU diagnostic buffer in STEP 7.

1. In HW Config, right-click the CP 342-5 and select PLC > Module Information.
2. Open the Diagnostic Buffer tab and look for events with IDs 16#0E40 (bus fault), 16#0E41 (DP slave failure), 16#0E42 (DP slave recovered), or 16#0E46 (parameter assignment error).
3. Open the Diagnostic Interrupt tab on the CPU and check for class-A entries tied to the CP.

Verification Procedure

Run each step in order and stop on the first failure.

1. In ProTool, open System > Status / Diagnosis. The connection should read "OK" with a cycle time under 200 ms for typical tag counts.
2. Create a test tag at a known address (e.g. MW 100 in DB 10) and bind it to a numeric I/O field on the panel.
3. Force a value in the PLC (VAT table or watch table) and verify the OP updates within 2 poll cycles.
4. Power-cycle the OP and verify automatic reconnection without operator intervention.
5. Disconnect the Profibus cable and re-attach - the OP should restore communication within 30 seconds without a project reload.
6. Read the CP diagnostic buffer one more time; it should contain no active error events.

Cross-Reference: Using CP 342-5 With Non-Siemens Devices

The CP 342-5 DP master can also poll non-Siemens DP slaves such as the Eaton SmartWire-DT gateway (EU5C-SWD-DP), drives, or third-party I/O. The procedure is identical from the ProTool side; only the GSD file and slot mapping change. This makes the same configuration procedure a useful starting point for adding remote I/O later without disturbing the existing HMI link.

Troubleshooting Matrix

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Frequently Asked Questions