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Replacing PROFIBUS DP Slaves with Different PNO Ident Numbers and GSD Files in SIMATIC PCS 7

Replacing PROFIBUS DP Slaves with Different PNO Ident Numbers and GSD Files in SIMATIC PCS 7

When replacing a legacy PROFIBUS DP slave (such as a KSB SMARTRONIC valve positioner with Ident Number 00CF) with a newer hardware revision (SMARTRONIC PC R1312 with Ident Number 051D), installing the new GSD file in STEP 7 HW Config does not alter or corrupt existing field devices. In PROFIBUS DP, each device type is uniquely identified by its 16-bit PNO Ident Number, allowing both revisions to coexist. However, the replacement device will not communicate until the new GSD slave is placed into HW Config at the designated DP address, compiled, and downloaded. In standard systems, downloading HW Config requires a CPU STOP unless Configuration in Run (CiR) was pre-configured.

Table of Contents

Executive Summary

Field device obsolescence is an inevitable reality in continuous industrial automation. When a legacy PROFIBUS DP field device (such as a KSB SMARTRONIC valve positioner) fails and is replaced with a modern revision (such as SMARTRONIC PC R1312), instrumentation engineers frequently discover that physically connecting the new device and setting the matching PROFIBUS address fails to establish communication; the bus fault (BF) LED remains blinking or steady red. Comparing device specifications reveals that the legacy valve had PNO Ident Number 0x00CF (configured via KSB_00CF.GSD), while the replacement features Ident Number 0x051D (using 051D.GSD). Engineers often worry whether installing a new GSD will disrupt existing operational valves on the bus, and whether a controller shutdown is required. This guide clarifies the PROFIBUS handshake principles and remedies.

PROFIBUS DP PNO Ident Number Architecture

In PROFIBUS DP (IEC 61158), every slave device possesses a 16-bit Ident Number assigned by the PROFIBUS Nutzerorganisation (PNO):

  • During startup, the DP Master issues a Set_Prm (parameterization) telegram containing the configured Ident Number.
  • The physical slave compares the telegram's Ident Number against its internal firmware.
  • If the numbers match, the slave accepts parameters and enters cyclic data exchange (Chk_Cfg).
  • If they differ (e.g. Master sends 0x00CF, but device is 0x051D), the slave immediately rejects parameterization and reports a configuration fault (BF), preventing all process data exchange.

GSD File Coexistence and Driver Independence

Installing a new GSD file via Options > Install GSD File in STEP 7 HW Config:

  • Places the new device description into the hardware catalog under PROFIBUS DP > Additional Field Devices.
  • Does NOT overwrite, replace, or alter any previously installed GSD files with different Ident Numbers.
  • Existing operational field devices (e.g. legacy positioners running 0x00CF) continue communicating with zero disruption.

Hardware Configuration Download: CPU STOP vs Configuration in RUN (CiR)

Modifying the PROFIBUS DP master system in HW Config requires a download:

  • Standard S7-400 / S7-400H without CiR: Downloading hardware configuration changes requires placing the CPU into STOP, requiring a planned plant maintenance outage.
  • S7-400 with Configuration in RUN (CiR): If a CiR object was previously inserted into the master system, slaves can be added, replaced, or modified without halting CPU execution or interrupting active processes.

Device Replacement Decision Matrix

The following table compares device replacement scenarios on an active PROFIBUS DP segment:

Replacement ScenarioIdent Number StatusGSD Action RequiredHW Config Download Required?Controller State ImpactIdentical Hardware ReplacementIdentical (0x00CF -> 0x00CF)NoneNo (Direct hot-swap)Bumpless hot-swap; no CPU impact.Firmware Revision (Diff Ident)Different (0x00CF -> 0x051D)Install 051D.GSDYes (Full HW Compile)CPU STOP (or CiR bumpless download).Profile Compatibility ModeCompatible (PA Profile 3.0)None (Uses Profile GSD)No (if profile matches)Bumpless hot-swap in profile mode.Add Coexisting New SlaveDistinct (0x051D)Install 051D.GSDYes (Add to new address)Requires CPU STOP or CiR download.

Step-by-Step Procedure to Install New GSD and Replace Slave

Method 1: Installing New GSD and Reconfiguring HW Config

  1. Download the authentic GSD file (e.g. 051D.GSD and bitmap .bmp) from the manufacturer's official support portal.
  2. Open HW Config in SIMATIC Manager with all station windows closed.
  3. From the menu bar, select Options > Install GSD File....
  4. Browse to the folder containing 051D.GSD and click Install.
  5. Select Options > Update Catalog to refresh the hardware tree.
  6. Open the station hardware configuration.
  7. Locate the old slave on the PROFIBUS DP master line. Note its assigned I/O addresses, diagnostic address, and DP address.
  8. Delete the old slave object (or change DP address if keeping for audit).
  9. From the hardware catalog (Additional Field Devices > Valves), drag the new SMARTRONIC PC 1312 onto the DP line.
  10. Assign the exact same DP node address and I/O address range so CFC block interconnections remain valid.
  11. Execute Station > Save and Compile.
  12. During an approved maintenance window, download the hardware configuration to the CPU.

Verification

To verify that the replaced field device is communicating properly:

  1. Bus Fault LED Audit: Inspect the replacement positioner. Confirm that the BF (Bus Fault) LED turns OFF, indicating active cyclic communication.
  2. HW Config Online Diagnostics: Go online in HW Config. Confirm that the slave icon displays no red slash or warning symbol.
  3. CFC Signal Verification: Open the associated valve CFC chart (VlvL / Pcs7AnIn). Confirm that live valve position feedback (PosReal) updates smoothly and channel driver reports quality code 16#80 (Good).

Limitations and Operational Precautions

  • Unplanned CPU STOP Risk: Never click 'Download to Module' in HW Config on an active production controller without confirming whether the CPU will be forced into STOP.
  • I/O Address Shifting: Ensure the new device's I/O module structure exactly matches the previous memory offsets to avoid corrupting CFC cross-references.
  • DP Address Switch Verification: Double-check that physical DIP switches or rotary dials on the replacement device match the configured node address before connecting to the bus.

Engineer FAQ

Can a field device have multiple Ident Numbers?

Some advanced devices support switching between a manufacturer-specific Ident Number and a standard PNO Profile Ident Number via onboard parameters.

Why did HW Config say 'Cannot install GSD file'?

GSD files must be installed while all HW Config station editing windows are closed.

Does installing a GSD file require an engineering license?

No. GSD files are open standard text descriptions defined by PROFIBUS International (PI) and require no software licenses.

Technical References

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