System Diagnostics for S7-300 SWR ET 200M: Configuration Guide

Overview of System Diagnostics in S7-300 Software Redundancy

System Diagnostics for the SIMATIC S7-300 Software Redundancy (SWR) configuration monitors the health of PROFIBUS DP slaves and the I/O modules installed behind them. When you run two S7-300 stations (or one S7-300 plus one S7-400) linked through a bus system with a redundant user program, the diagnostic view extends to every ET 200M station connected to either CPU via PROFIBUS DP. The diagnostic chain covers three layers:

1. Interface Module (IM 153-2 / IM 153-4) operating state and backplane status.
2. Signal Module (SM 321 / SM 322 / SM 331 / SM 332) presence, type identification, and parameterization errors.
3. Channel-level faults on the SM itself, including wire break, short circuit, and out-of-range values.

System Diagnostics is delivered as a separate optional package within the STEP 7 V5.x environment and is functionally distinct from the ProAgent/ProTool/Pro diagnostics chain that targets HMI panels. It exposes standardized diagnostic data through System Status Lists (SSL) and Standard Diagnostic Data (DD) records that any SCADA front-end can consume, including IEC-104-based systems such as VICOS OC.

Supported Hardware Matrix for S7-300 SWR + ET 200M Diagnostics

Verify the catalog number against the Siemens SIMATIC S7-300 Module Data manual before commissioning; diagnostics support varies by hardware revision even within the same MLFB.

How SWR Reports Diagnostics from ET 200M Stations

The S7-300 SWR package reserves PROFIBUS DP slots on each CPU for partner-CPU handshaking and replicates the process image. Diagnostic events from ET 200M stations propagate identically to both redundant CPUs because the SWR user program accesses the same logical DP addresses regardless of which physical CPU is currently MASTER. When the standby CPU takes over, OB 70 (CPU redundancy error) or OB 83 (pull/plug) is triggered on the new master, and the diagnostic buffer receives a timestamped entry.

For more detail on the underlying redundancy architecture, see the Siemens reference Software redundancy for SIMATIC S7 (PDF). The S7-1500R/H documentation describes the equivalent mechanism for the newer platform; while the CPU generation differs, the conceptual handling of Loss of redundancy CPU events documented at TIA Portal: Loss of redundancy CPU confirms that OB 70 / OB 86 handling patterns apply to both generations.

System Diagnostics Package Installation and Licensing

The optional System Diagnostics package installs under Start > SIMATIC > STEP 7 > System Diagnostics once the licensed setup runs. It is licensed separately from STEP 7 and from the SWR option (order number 6ES7862-1AC00-0YA5 for SWR V2.x). Activation requires:

1. Insert the System Diagnostics CD into the engineering station.
2. Run Setup.exe as administrator and select the matching STEP 7 V5.x version.
3. Transfer the license key to the local USB license dongle or hard-disk key using the Automation License Manager.
4. Restart the STEP 7 SIMATIC Manager; the System Diagnostics node appears under the S7 project.

Reading Channel-Level Diagnostics from Standard S7-300 I/O

Channel-level diagnostics are available on standard S7-300 SM modules provided the diagnostic interrupt is enabled in HW Config and OB 82 is loaded on the CPU. The procedure is as follows:

1. Open the ET 200M station in HW Config and select the SM (e.g., SM 331 AI 8x12 Bit).
2. In the Inputs tab, set Diagnostic Interrupt = Enabled for each channel where wire break or overflow detection is needed.
3. Confirm that Hardware Interrupt is configured for the upper/lower limit if process alarms are also required.
4. Download the HW Config to both redundant CPUs.
5. Insert OB 40 (hardware interrupt) and OB 82 (diagnostic interrupt) into the offline block container; both must exist or the CPU goes into STOP on the first fault.

When the SM raises a channel fault, the operating system writes a standardized diagnostic record starting at byte 0 with the following structure (per EN 50170 / IEC 61158):

Call SFC 13 "DPNRM_DG" in OB 82 with the slot address from OB82_MDL_ADDR to read the full record into a user DB:

CALL "DPNRM_DG"
  REQ       := TRUE
  LADDR     := #stat_LADDR         // W#16#0xxx from OB82_MDL_ADDR
  RET_VAL   := #stat_RetVal
  RECORD    := P#DB100.DBX 0.0 BYTE 32
  BUSY      := #stat_Busy
END_CALL

Line Monitoring on Standard S7-300 Digital Modules

Line monitoring — automatic detection of wire break, sensor supply short circuit, or load voltage loss on individual channels — is implemented as a subset of channel-level diagnostics and is only present on certain SM 321 / SM 322 variants.

Confirm the catalog number is one of the variants supporting line monitoring. If the module is the standard SM 321-1BH02 without NAMUR, wire break cannot be reported at channel granularity; only a loss of process voltage at the module terminals is announced as a module-level diagnostic.

Integrating Diagnostics with VICOS OC over IEC-104

VICOS OC is the ABB substation controller SCADA front-end used in energy and traction substations. It does not consume Siemens S7 proprietary diagnostics directly; it expects IEC 60870-5-104 information objects mapped to internal data points. The pattern below extracts diagnostics into a STEP 7 DB and exposes the bits over IEC-104.

1. Define a global diagnostic DB (e.g., DB 200) with one DWORD per ET 200M slot and one BOOL per channel fault.
2. Program OB 82 to set the bit corresponding to the faulty slot/channel and write a timestamp from OB82_DATE_TIME.
3. Cycle the data through an S7 communication block — typically PUT/GET to an S7-400 protocol gateway running IEC-104 firmware (e.g., ABB RTU 560 series or SAT 143).
4. Map the DB bits to IEC 104 ASDUs in the gateway configuration:

The CP56Time2a format used by IEC-104 is a 7-byte BCD timestamp. Build it from OB82_DATE_TIME using the standard Siemens date-and-time conversion functions (FC 6 / FC 7) before writing to the gateway DB.

System Status List (SSL) Partial Lists Used by SWR Diagnostics

SFC 51 ("RDSYSST") provides indexed access to the partial system status lists that contain diagnostic information about modules and racks. The following SSL IDs are particularly relevant for SWR + ET 200M diagnostics:

CALL "RDSYSST"
  REQ       := TRUE
  SSL_ID    := W#16#0B2                 // Module status
  INDEX     := W#16#0008                // Slot 8
  RET_VAL   := #stat_RetVal
  BUSY      := #stat_Busy
  SSL_HEADER:= P#DB201.DBX0.0 BYTE 4
  DR        := P#DB201.DBX4.0 BYTE 32
END_CALL

Step-by-Step Commissioning Procedure

1. Hardware check: Confirm both redundant CPUs, both IM 153-2 modules (one per ET 200M), and all SMs are seated and bolted. Verify PROFIBUS termination at both cable ends with the standard Siemens PROFIBUS connector (6ES7972-0BA12 with PG socket, or 6ES7972-0BB12 with diagnostics LED).
2. HW Config upload: Open STEP 7 SIMATIC Manager, connect online to each CPU, and run PLC > Upload Station to PG to capture the actual configuration. Compare against the offline project.
3. Enable diagnostic interrupts: For every SM where channel-level diagnostics are required, open the module properties and tick Diagnostic Interrupt. Save and download to both CPUs.
4. Load OB 82 and OB 86: Insert OB 82 (diagnostic interrupt) and OB 86 (rack failure) into the offline project. If SWR is configured, also load OB 70 (redundancy error) and OB 83 (pull/plug). At minimum OB 82 must be present; the CPU otherwise enters STOP on the first diagnostic event.
5. Build diagnostic DBs: Create DB 200 (bit-mapped module status) and DB 201 (SSL header + data buffer). Cross-reference each bit to the channel number from the HW Config diagnostic address list.
6. Configure System Diagnostics package: If ProAgent HMI blocks are needed, open the project node System Diagnostics, click Generate Block, and assign the resulting FB 126 / FB 127 to the OB 82 call.
7. Wire DB bits to IEC-104 gateway: Configure PUT/GET access rights in the CPU properties (no password for the gateway partner). Build the IEC-104 point list in the gateway's configuration tool using the bit-to-ASDU table above.
8. Force test fault: Remove a digital input wire to simulate wire break. Verify that DB 200 updates, OB 82 executes, the gateway reports the change to VICOS OC, and the timestamp is present in the IEC 104 event list.

Verification Checklist

• OB 82 executes on both CPUs; diagnostic buffer entries are timestamped and identical in content.
• DB 200 reflects the active fault within one OB 82 cycle (typically < 50 ms).
• VICOS OC event log shows the corresponding IEC 104 information object with CP56Time2a timestamp accurate to 1 ms.
• Loss of a complete ET 200M station triggers OB 86 with OB86_EV_CLASS = B#16#39; DB 200 marks the slot as station failed.
• Standby CPU takes over within the SWR watchdog window (default 400 ms) and continues diagnostics without operator intervention.
• CPU diagnostic buffer can be read via SFC 51 ID 0132 in CSV for offline post-mortem.

Troubleshooting Matrix

FAQ