Resolving S7-300 to Omron CIMR-VC4A0009BAA PROFIBUS Bus Fault

Problem Overview

A Siemens S7-300 CPU (with CP 342-5 PROFIBUS DP master or integrated DP port) is supervising 25 Omron inverters on a water-bottling conveyor through a PROFIBUS DP daisy chain. The original drives, CIMR-V7AZ40P7 (V7 series, 400 V class, 0.75 kW range), are obsolete and out of production. Omron has supplied the replacement CIMR-VC4A0009BAA (V1000 series, 400 V class, 3.7 kW / 9 A frame). When the new V1000 is inserted in the 4th physical position of the chain, the S7-300 reports a PROFIBUS bus fault (SF/BF) on the inserted drive and on every slave downstream of it, while the three upstream drives continue normal cyclic data exchange.

This symptom is the classic signature of a slave-side PROFIBUS termination, address, or GSD mismatch rather than a CPU, cable, or master fault, because the fault window is strictly bounded by the offending node position. The complete diagnostic flow below is the field-proven sequence for isolating the root cause in less than 30 minutes per node.

Hardware and Software Prerequisites

Before opening STEP 7 or touching the V1000, confirm the following are present on site:

• Omron SI-P1 PROFIBUS-DP option card (3G3AX-SI-P1) installed in option port CN5 of the CIMR-VC4A0009BAA. The V1000 does not have a built-in PROFIBUS interface; without SI-P1 the drive cannot appear on the bus regardless of GSD configuration.
• GSD file for the V1000 with SI-P1 (Omron filename typically OMR0918B.GSD or OMR0918.GSD; check the Omron MX2/V1000 PROFIBUS option kit manual for the exact revision matching the drive's SI-P1 firmware).
• STEP 7 V5.5 + SP2 (or later) with the hardware catalog update for the V1000 PROFIBUS slave. TIA Portal V13 SP1+ is acceptable for S7-300 firmware V3.x and later, but the original commissioning team used SIMATIC Manager.
• Siemens MPI/PC Adapter USB (6ES7 972-0CB20-0XA0) or Ethernet CP for online access to the S7-300.
• Omron CX-Drive (V2.5 or later) to read/write V1000 parameters and verify H5-xx PROFIBUS settings without an online connection.

Root Cause Analysis

Five independent failure modes can produce the exact fault pattern observed (downstream slaves drop, upstream slaves stay alive). Treat them in the order shown because each test invalidates the ones below it.

Pre-Commissioning Verification on the V1000 Keypad

Before the drive is connected to the running bus, perform these keypad checks. This isolates the drive in 5 minutes without disturbing the production line.

1. Power the V1000 only (do not connect the PROFIBUS cable). Apply 400 V three-phase to L1/L2/L3.
2. Verify the keypad is in Drive Mode (not Program). Press LO/RE until the green REM light is OFF (local control) for the next test only; for PROFIBUS control return to REM.
3. Navigate to U1-06 (Option Card Connected). It must read "SI-P1" or "PB". A reading of "---" means the SI-P1 card is not seated correctly in CN5; remove and reseat, or check the card's CN5 connector for bent pins.
4. Read U1-15 (Option Card Frequency Reference / Status Word). This confirms the card is communicating with the drive's internal logic even before PROFIBUS is connected.
5. Set node address: parameter H5-01. Default is 1F (hex) = 31 decimal. Change to the address that the V1000 will occupy in the chain (for example, 4 to replace the 4th V7AZ). Range: 0–125. Save by pressing ENTER.
6. Set baud rate: H5-02. The V1000 PROFIBUS card auto-detects baud rate from the master; the parameter is informational. Confirm the rest of the chain runs at 1.5 Mbit/s (default) or 12 Mbit/s if previously configured; do not mix baud rates in one segment.
7. Set loss-of-communication timeout: F6-02 = 2.0 s and response F6-03 = 1 (continue last reference). The V1000 default of 0 (instant fault) will trip the drive on the first bus scan; this is the most common reason a newly inserted V1000 reports fault CE and pulls down downstream nodes.
8. Set PROFIBUS reference source: b1-01 = 3 (PROFIBUS reference) and PROFIBUS run source: b1-02 = 3 (PROFIBUS run/stop). Without these two parameters the drive will run from analog/keypad regardless of the cyclic control word from STEP 7.
9. Set drive scaling: o1-03 = 0 (display Hz); o1-04 = 0 (units = 1). These are not strictly required for communication but eliminate confusing keypad readouts during commissioning.

Installing the V1000 GSD File in STEP 7

The replacement drive cannot be commissioned until the correct GSD is installed in the S7-300 hardware catalog. The original GSD for V7AZ must remain installed if the other 24 drives are still V7AZ units; PROFIBUS allows mixed slaves on a single segment, but the master must know each slave's identifier number and configuration.

1. Copy the V1000 GSD file (for example, OMR0918B.GSD) and the matching bitmap (OMR0918B.BMP) into C:\Program Files\Siemens\Automation\SIMATIC Manager\S7DATA\GSSE (or the equivalent S7hconfig path on the engineering station).
2. Close all instances of SIMATIC Manager. Reopen the project.
3. In HW Config, choose Options > Install GSD File..., browse to the V1000 GSD, and confirm. The new device appears in the catalog under PROFIBUS DP > Additional Field Devices > Drives > Omron > CIMR-VC V1000.
4. Open the PROFIBUS(1) subnet properties and verify the master address (S7-300 CPU) is 2 and the baud rate matches the chain (1.5 Mbit/s is the safe default for 25 nodes on standard PROFIBUS cable).
5. Delete the old DP slave object at the address of the failed V1000 (it is still configured as a V7AZ). Confirm before deletion; this also drops the symbolic I/O names for that drive and forces an OB82 / OB86 hit at download time, which is normal.
6. Drag the new CIMR-VC V1000 PROFIBUS from the catalog onto the PROFIBUS(1) line. Assign the same address (for example, 4) that the drive's H5-01 is set to.
7. Double-click the slave to open its properties. Select the slot configuration: PPO Type 1 (4 PKW / 2 PZD) is the conventional choice for V1000 speed control. PPO Type 3 (0 PKW / 2 PZD) is acceptable if the application only writes setpoint and reads status, but PKW is required for reading/writing parameters from STEP 7 via the SFC58/59 or SFB52/53 record mechanism.
8. Map the I/O addresses. Conventional mapping for V1000 PPO Type 1:
   PIW 256 = Status Word 1
   PIW 258 = Actual Frequency (Hz × 100)
   PQW 256 = Control Word 1
   PQW 258 = Frequency Reference (Hz × 100)
   (Offset values depend on the slot's base; adjust to avoid overlap with V7AZ slots on other addresses.)
9. Compile and download HW Config (target system → CPU 31x → download). The CPU will go STOP briefly if S7-connection resources are not pre-configured; this is normal for the first PROFIBUS configuration download.

Bus Termination and Physical Layer

PROFIBUS DP is a single-trunk RS-485 topology. Each segment must have exactly two terminations, one at each physical end of the cable run, with all intermediate nodes having termination OFF.

• Locate the SI-P1 card's onboard terminator. It is a 2-position slide switch labelled ON / OFF on the top edge of the SI-P1 module. Default from Omron is OFF.
• For a V1000 placed in the 4th position of a 25-node daisy chain, the termination must be OFF. Only the 1st and 25th physical nodes have termination ON.
• Use Siemens PROFIBUS bus connector 6ES7 972-0BA12-0XA0 (with PG socket, 90° cable outlet) on the upstream side, and 6ES7 972-0BA50-0XA0 (without PG socket) on the downstream side, with the integrated switch on the connector itself set correctly.
• Verify shield continuity. The PROFIBUS cable shield must be clamped 360° at every connector. A pinched or lifted shield at the new V1000 connector can float the bus reference and produce intermittent BF events.
• Measure the bus voltage between pins 3 (B-line) and 8 (A-line) at the new V1000 with the PLC in RUN. Healthy value: 4.75–5.25 V DC. Below 4.5 V indicates a termination missing upstream, an extra termination, or a shorted cable.

Diagnostic Procedure Using Accessible Nodes

Accessible Nodes is the fastest online test to prove the GSD is recognized and the physical layer is intact.

1. Connect the MPI/PC Adapter to the S7-300 MPI port (not the PROFIBUS port). Set the PC interface in Set PG/PC Interface to PC Adapter (Auto) / MPI.
2. In SIMATIC Manager, choose PLC > Accessible Nodes. After a few seconds the online view lists every node that responds on the MPI subnet (the CPU only — the S7-300 MPI port is not the same physical network as PROFIBUS DP).
3. Switch the PC adapter to PC Adapter (Auto) / PROFIBUS and repeat. This time Accessible Nodes lists every DP slave that the master can see, including the V1000 with the correct station number if the GSD, address, and termination are correct.
4. If the V1000 is not listed, the fault is physical (termination, cable, address) or the SI-P1 is not running (check U1-06).
5. If the V1000 is listed but marked with a yellow diagnostic icon, the GSD slot configuration does not match what the drive is offering. Read the diagnostic buffer (PLC > Diagnostics/Setting > Module Information) for the exact DP slave diagnostic bytes; the standard PNO error codes are decoded in the table below.

Isolating a Single New Drive on a Test Bench

If the fault persists after the steps above, the next level of isolation is to remove the new V1000 from the daisy chain and commission it on a stand-alone PROFIBUS segment with the S7-300. This proves the drive is functional and isolates whether the issue is from interaction with the other 24 V7AZ drives.

1. Build a minimal STEP 7 project containing only the S7-300 CPU and a CP 342-5 (or use the CPU's integrated DP port). Add the V1000 as the sole DP slave at address 4.
2. Connect the CPU's DP port directly to the V1000's SI-P1 with a single PROFIBUS cable and bus connector with termination ON at the V1000 only.
3. Download the project. The V1000 should appear in Accessible Nodes within 5 seconds. If it does, the GSD, cable, drive, and SI-P1 are all healthy; the original bus fault is due to interaction with the existing chain (most often a missing termination at a damaged V7AZ that the new V1000 cannot compensate for).
4. If the drive still does not appear, the SI-P1 card is suspect. Swap the card with the one from another V1000, or with a known-good spare, and repeat.

Replacing All 25 V7AZ Drives with V1000 Units

After the first V1000 is proven, the rest of the fleet can be rolled out. The recommended sequence avoids stopping the water plant more than one drive position at a time.

1. Stage all 25 V1000 units on the bench. Pre-configure H5-01, b1-01, b1-02, and F6-02/03 on each unit. Record the mapping from serial number to node address.
2. Update the STEP 7 HW Config in a single engineering change: delete each V7AZ DP slave object and insert a V1000 in its place with the same address and the same PZD offset. This keeps the user program (FC/FB blocks reading PIW 256, etc.) untouched only if the V1000 PZD mapping is identical to the V7AZ. Confirm in the V7AZ GSD documentation that the PZD word order and scaling match; if not, a parameter remap in the user program is unavoidable.
3. Perform the swap during a scheduled conveyor stop, one drive at a time, starting with the end-of-line drive (25th) and walking back to node 2. This keeps the chain live with as many slaves as possible at every step.
4. After each swap, confirm Accessible Nodes shows the new V1000 at the expected address with no SF/BF on the CPU and no diagnostic alarms in the buffer.
5. Keep at least one fully configured V1000 with the bench GSD and parameter set on the shelf as a cold spare. Keep one V7AZ with its GSD in HW Config commented out but present in the source so a legacy spare can be brought back online within 30 minutes if a V1000 fails before the fleet is fully matured.

Verification and Acceptance Criteria

After the swap, verify the following signals in S7-300 to confirm PROFIBUS health:

• CPU BF LED: OFF (green) for the integrated DP port; OFF for CP 342-5.
• CPU SF LED: OFF.
• Diagnostic buffer: no new DP diagnostic entries after 1 hour of operation.
• Cyclic data: the user program reads the actual frequency from PIW and writes a non-zero setpoint to PQW; the V1000 keypad shows the same setpoint in U1-15 and the motor rotates at the commanded speed.
• Bus voltage: measured between pins 3 and 8 of the new V1000 connector with the CPU in RUN, 4.75–5.25 V DC stable.
• Comm-loss behaviour: physically unplug the PROFIBUS cable from the new V1000; the drive must not trip immediately. With F6-02 = 2.0 s, the drive continues at the last reference for 2 seconds, then executes F6-03 (continue, coast, or ramp to stop). Reconnect the cable; communication must resume without a CPU restart.

Troubleshooting Matrix

FAQ