CP342-5 and IM155-6DP Communication Fault DPV0 vs DPV1 Resolution

1. Problem Overview

When commissioning an ET 200SP station built around an IM 155-6DP head module (firmware V4.2 and higher) on a Siemens CP 342-5 communications processor (firmware V6.0.66) programmed with STEP 7 V5.6 SP2, two distinct symptoms occur during HW Config setup:

1. GSD-based configuration path: The IM 155-6DP station is added via its GSD file (SIEM81D2.gsd or vendor-specific variant), but the CP 342-5 reports a bus fault — the BF (Bus Fault) LED on the CP illuminates and the slave is not visible in the online diagnostics, even though HW Config shows a valid PROFIBUS address and slot assignment.
2. Hardware catalog (HSP) configuration path: When the IM 155-6DP is selected from the STEP 7 catalog profile (installed via the latest Hardware Support Package), the project fails to compile or save with the diagnostic: "The inserted slave requires a DPV1 master."

Both symptoms share a single root cause: a DPV0 / DPV1 protocol mismatch between the master and slave. The CP 342-5, regardless of its catalog version, is a DPV0 master; the IM 155-6DP station exposes a slot-0 interface that requires DPV1 services for the standard ET 200SP diagnostic and parameterization model.

2. Hardware Identification and Catalog Numbers

Confirm the exact part numbers in your rack and on the head module before applying any of the procedures below. The CP 342-5 ships in several firmware releases, and the IM 155-6DP exists in multiple variants within the ET 200SP family.

Reference: Siemens CP 342-5 product page (Entry ID 8773895) and ET 200SP IM 155-6DP manual (Entry ID 109478763).

3. Root Cause: DPV0 vs DPV1 Incompatibility

PROFIBUS DP defines three protocol generations on the same physical RS-485 layer:

• DPV0 — cyclic I/O data exchange, no acyclic services. Sufficient for classic ET 200M, ET 200S, ET 200B stations.
• DPV1 — adds acyclic read/write services (MS0/1/2) and extended diagnostics. Required by modern Siemens head modules to expose module parameters, port statistics, and channel-granular diagnostics.
• DPV2 — adds equidistance and slave-to-slave broadcast; not in scope for this article.

The CP 342-5 implements the DPV0 master state machine. During the start-up phase, it performs GetCfg / ChkCfg sequences against the slave. When the IM 155-6DP (V4.2 and higher) responds with a DPV1-tagged identifier byte and expects an MS0 connection setup in the parameterization telegram, the CP 342-5 cannot satisfy the request. The result is either a silent ChkCfg rejection (BF LED) or a hard compile-time refusal when the ET 200SP HSP is used, because the HSP explicitly checks the master class property.

Diagnostic confirmation path:

1. In HW Config, right-click the CP 342-5 and select Properties → Operating Mode. The dialog only allows DP Master or DP Slave; there is no DPV1 tick box. This is the visual confirmation that the master is DPV0.
2. Read the BF LED pattern. Steady BF on the CP with a missing station at the expected PROFIBUS address indicates start-up fault, not wiring. A flashing BF (1 Hz) indicates parameterization error — typical of the DPV0/DPV1 mismatch.
3. Online → Accessible Nodes on the CP 342-5 (via the S7-300 CPU routing) will not list the IM 155-6DP. This rules out cable/termination issues.

4. STEP 7 V5.6 SP2 Configuration Errors Explained

4.1 Catalog Path (HSP) Error

When you add the IM 155-6DP from the PROFIBUS DP → ET 200SP branch of the STEP 7 V5.6 SP2 catalog, the HSP carries a SLAVE_TYPE = DPV1 attribute. The CP 342-5 object in the master slot carries a MASTER_TYPE = DPV0 attribute. STEP 7 performs a static link check on save/compile and emits:

Error:  Slave at DP master system 1, address X requires DPV1 master services.
       The selected CP 342-5 (6ES7 342-5DA02-0XE0) only supports DPV0.
       Insert a DPV1-capable master (e.g. CPU 31x-2 DP, CP 343-5, IM 157).

Choosing a different host CPU (e.g., 315-2 DP) is irrelevant because the CP 342-5 is the master in this configuration, not the CPU.

4.2 GSD Path Silent Failure

When the IM 155-6DP is installed via GSD, STEP 7 does not perform the DPV0/DPV1 cross-check at compile time. However, the resulting compiled project writes DPV0-only parameterization telegrams to the CP. The IM 155-6DP rejects the parameterization and never enters cyclic data exchange. From the user program side, the CP 342-5 reports the slot as failed, and FC1/DP_SEND returns an error code in its ERROR and STATUS outputs.

5. Solution Path A — GSD-Based Configuration with FC1/FC2

This is the documented and field-confirmed resolution for the DPV0 master / DPV1-capable slave combination.

5.1 Install the GSD File

1. Download the GSD package for the IM 155-6DP from Siemens Entry ID 109478763. The GSD filename pattern is SIEM81D2.gsd (older FW) or GSDML-Vx.x-xxxx-ET200SP-IM155-6DP-yyyymmdd.xml (newer PROFINET-style files for PROFIBUS DP variants are not used; the PROFIBUS GSD remains the .gsd file).
2. Close all STEP 7 instances. Copy the SIEM81D2.gsd and the associated bitmap/Notebook files into ...\Siemens\Step7\S7DATA\GSD\.
3. Restart STEP 7 Manager. In HW Config, choose Options → Install GSD File. The IM 155-6DP appears under PROFIBUS DP → Other Field Devices → ET 200SP (or Siemens I/O).

5.2 Insert the Slave in HW Config

1. Open the S7-300 station containing the CPU 313C and the CP 342-5.
2. Set the CP 342-5 as DP Master with the desired PROFIBUS address (typically 2).
3. From the installed GSD branch, drag the IM 155-6DP to the master system at an unused address (e.g., 3).
4. Add at least one I/O module slot (e.g., DI 8x24VDC HF, 6ES7 131-6BF00-0BA0) and one DO module slot to make the configuration non-empty — an empty IM 155-6DP slot-0 will be rejected by the CP at startup.
5. Save and compile. STEP 7 accepts the project because the GSD path skips the DPV1 master cross-check.

5.3 Program FC1 / FC2 in the S7-300 CPU

The CP 342-5 does not auto-exchange data. You must call the Siemens-supplied DP_SEND and DP_RECV functions in the user program (OB1, OB82, OB86, or OB100 as appropriate). These are part of the CP 342-5 / CP 343-5 library installed with STEP 7 V5.x:

ST example for OB1:

// DP_SEND call (FC1) — write outputs to IM 155-6DP via CP 342-5
CALL "DP_SEND" , "I_DB_DP_SEND"
  CPLADDR  := W#16#100   // Logical base address of the CP 342-5
  SEND     := P#DB100.DBX0.0 BYTE 16   // 16 bytes of output image
  DONE     := M 100.0
  ERROR    := M 100.1
  STATUS   := MW 102;

// DP_RECV call (FC2) — read inputs from IM 155-6DP via CP 342-5
CALL "DP_RECV" , "I_DB_DP_RECV"
  CPLADDR  := W#16#100   // Same CP base address
  RECV     := P#DB200.DBX0.0 BYTE 16   // 16 bytes of input image
  NDR      := M 110.0
  ERROR    := M 110.1
  STATUS   := MW 112
  DPSTATUS := MB 114;

Key parameter notes:

• CPLADDR must match the logical address assigned to the CP 342-5 in HW Config. For a CP 342-5 in slot 4 of an S7-300 rack, the default base address is commonly W#16#0100 (256 decimal). Verify with HW Config → CP 342-5 → Properties → Addresses.
• SEND / RECV pointer areas must match the I/O length configured in the IM 155-6DP slot assignment (e.g., 2 bytes input + 2 bytes output for a 16-channel DI/DQ module pair).
• Call the blocks from OB100 (restart) first to perform an initial handshake, then from OB1 cyclically.

6. Solution Path B — Alternative DPV1-Capable Masters

If the application requires the IM 155-6DP catalog profile and full DPV1 acyclic services (e.g., for port-level diagnostics, firmware updates via PROFIBUS, or RDREC / WRREC access from the user program), replace the CP 342-5 with one of the following masters:

Reference: Siemens Entry ID 8859629 — SIMATIC NET PROFIBUS masters comparison.

7. Diagnostic and Verification Procedures

After applying the GSD path with FC1/FC2, verify the link in this order:

1. Hardware LEDs on the CP 342-5: SF off, BF off. If BF flashes, parameterization is still rejected — re-check slot consistency.
2. Hardware LEDs on the IM 155-6DP: PWR green, BF off, ACT green flashing. A steady BF on the head module indicates the master is not transmitting acyclic parameterization frames the IM expects.
3. Online diagnostics in STEP 7: Right-click the CP 342-5 master system → PROFIBUS → Diagnostics. The IM 155-6DP should appear with status OK and a green check on every configured slot.
4. FC1/FC2 status words: After one OB1 cycle, STATUS should read W#16#0000 (no error) for both DP_SEND and DP_RECV. Common error codes:
   • W#16#000A — DP_SEND/RECV: data consistency error (call from OB1 only, not from multi-instance contexts without attention to byte alignment).
   • W#16#80B0 — Slave not reachable; check PROFIBUS termination and address.
   • W#16#80C1 — Configuration error; the slot list in the GSD does not match the physical module insertion.
5. Forced test: Toggle an output bit mapped to the IM 155-6DP DQ module and confirm the corresponding LED on the module. This validates end-to-end cyclic exchange.

8. Troubleshooting Matrix

9. STEP 7 V5.6 SP2 HSP and GSD Compatibility Notes

Hardware Support Packages for STEP 7 V5.x are version-bound. The latest HSP for the ET 200SP family is HSP 2022 or later. Installing an HSP that catalogs the IM 155-6DP under ET 200SP will cause the DPV1 requirement error when the master is a CP 342-5. The recommended field practice is:

1. Install the GSD file for the IM 155-6DP only, do not enable the corresponding HSP section.
2. Maintain a separate, version-controlled folder of GSD files for all DPV0/DPV1 hybrid installations.
3. If a project must be migrated to TIA Portal in the future, re-evaluate the master; a CP 342-5 will not be supported in TIA Portal as a new configuration, and the IM 155-6DP is typically re-paired with a S7-1500 CPU with integrated DP interface or a CM 1542-1/CM 1542-5 module.

10. Safety and EMC Field Notes

Although PROFIBUS DP is a robust industrial fieldbus, observe the following during commissioning:

• Terminate both ends of the segment only. Termination on a CP 342-5 is enabled via a slide switch on the front of the module; on the IM 155-6DP, terminations are handled inside the head and activated through STEP 7 or the IM's DIL switch.
• Use a shielded PROFIBUS cable with 9.6 kbit/s to 12 Mbit/s capability (e.g., Siemens 6XV1 830-0EH10). Ground the shield at both ends with low-impedance bonding.
• Maintain a minimum of 0.5 m clearance between PROFIBUS cables and VFD output power cables routed in parallel.
• Do not hot-swap I/O modules on the IM 155-6DP under PROFIBUS DPV0 when the CP 342-5 is in run — DPV0 does not natively support hot-swapping, and module removal will trigger a station failure.

11. Frequently Asked Questions