Siemens WF723A WinAC RTX Slot PLC: COM 723 Setup, Configuration, and Troubleshooting

1. WinAC RTX Slot PLC Architecture Overview

The Siemens WF723A is a member of the WinAC (Windows Automation Center) RTX slot PLC family — a class of PC-based controllers in which the deterministic real-time runtime executes on a dedicated hardware module installed inside an industrial PC, rather than as a purely software-based virtual controller. The slot PLC approach separates the Windows-based engineering environment and HMI from the deterministic PLC runtime, addressing the historical concern that a Windows crash would halt a Software Controller running on the host OS.

Architecturally, the WF723A combines:

• An integrated S7-CPU runtime compatible with the S7-300 instruction set, typically operating as the functional equivalent of a CPU 315-2 DP.
• A PROFIBUS DP master/slave interface on the slot module for distributed I/O.
• A PCI (or PC/104-plus on industrial variants) host interface for communication with the host PC's STEP 7 engineering software, OPC server, and HMI applications.
• Deterministic isolation from the host Windows OS through a dedicated real-time subsystem, often implemented with the Venturcom RTX (Real-Time eXtension) kernel.

This makes the WF723A attractive in installations that require both PC-based visualization or data logging and PLC-grade determinism, particularly in legacy S7-300 codebases that predate TIA Portal migration.

1.1 Slot PLC vs. Software Controller vs. Open Controller

Siemens historically offered three PC-based controller concepts. Understanding the differences clarifies where the WF723A fits in a control hierarchy:

The slot PLC positioning — installed in a ruggedized industrial PC (such as a SIMATIC Rack PC or SIMATIC Box PC) — gives the WF723A a distinct lifecycle. It is not a soft PLC, even though the project engineering is identical to a software controller. This distinction is critical when sizing PC hardware, planning OS patching windows, and designing fail-safe behavior.

2. WF723A Hardware Identification and Variants

Before installing COM 723, the engineer must confirm the exact variant of slot PLC installed in the host PC. The label on the module and the BIOS/PCI enumeration in the host operating system both report the Siemens order number (MLFB) and hardware revision.

2.1 Typical Order Numbers in the WF723 Family

The WF723 slot PLC family historically shipped in the following variants (consult the module's faceplate label for the exact order number before commissioning):

• WF723A — Standard PROFIBUS DP master/slave slot PLC, S7-300 instruction set, binary/floating-point operations.
• WF723A-PN — Variants equipped with PROFINET interface for distributed I/O on Industrial Ethernet.
• WF723B / WF723C — Later revisions with expanded work memory, larger data areas, and faster bit-operation throughput.

2.2 Required Host PC Architecture

Because the WF723A is a PCI/PC-104 module, the host industrial PC must be selected to accept the form factor. Legacy SIMATIC hosts such as the SIMATIC PC IL 40, SIMATIC PC IL 70, SIMATIC Box PC 620, and SIMATIC Rack PC 840 were certified for WinAC slot PLCs. Third-party industrial PCs were also widely deployed provided the chipset, BIOS, and PCI slot implementation conformed to the WinAC RTX hardware compatibility list.

3. COM 723 Software Role and Components

COM 723 is the Siemens commissioning and configuration tool dedicated to the WF723A slot PLC. It is not a replacement for STEP 7 — the project logic, hardware configuration of the distributed I/O, and symbol tables remain in STEP 7. COM 723 fills the specific gap that STEP 7 alone cannot address:

1. Configuring the RTX real-time subsystem and isolating the WF723A runtime from the host Windows process scheduler.
2. Installing, updating, and rolling back the slot PLC firmware (the equivalent of an operating-system update on the card).
3. Defining IP / PROFIBUS parameters, slot addressing, and the host↔slot communication channels (MPI/TCP or named pipe).
4. Creating a backup image (wiederherstellungs image) that can restore a corrupted slot PLC to a known-good firmware and configuration state — the only supported recovery path if the module's flash is damaged.
5. Reading diagnostic logs from the RTX subsystem (boot log, fault buffer, PROFIBUS diagnostic frames).

COM 723 is therefore best understood as the BIOS/firmware management utility for the WF723A, analogous to a storage-controller HBA configuration utility. It is invoked once during commissioning, then again whenever firmware is updated or the RTX subsystem is reconfigured. It is not part of the runtime path and does not need to remain open during production.

3.1 Component Layers

4. System Prerequisites

Installing COM 723 without verifying prerequisites is the single most common cause of failed commissioning. The full prerequisite list must be confirmed before touching the host PC.

4.1 Hardware Prerequisites

• Siemens-certified industrial PC with a free PCI (or PC-104-plus, depending on module) slot.
• WF723A slot PLC physically seated, with chassis screw secured and host PC powered down during installation.
• At least 512 MB RAM on the host beyond Windows requirements; 1 GB recommended.
• RS-232 or USB-to-PROFIBUS adapter for connecting STEP 7 to the slot PLC for project download.

4.2 Software Prerequisites

• STEP 7 V5.x (V5.4 SP5 or later recommended; SP versions are variant-dependent). Engineering projects for the WF723A cannot be created in TIA Portal — STEP 7 classic is mandatory.
• Microsoft Windows XP Professional SP3, Windows 7 Professional/Ultimate (32-bit preferred), or a Windows variant on the Siemens compatibility list for the specific WF723A order number.
• Venturcom RTX runtime matching the COM 723 release notes (typically installed automatically by COM 723 but listed here because the OEM version must be present if the host is rebuilt from image).
• Local administrator credentials on the host — RTX installs a kernel-mode driver and requires privilege elevation.

4.3 Licensing Prerequisites

COM 723 is licensed Siemens software and is delivered with the WF723A module on the original Siemens installation media (or via the Siemens Software Delivery Service for entitled users). The license key is keyed to the slot PLC's serial number. Plan the license transfer before decommissioning or replacing the host PC.

5. Installation Procedure for COM 723

The following procedure assumes the host PC is freshly imaged with a Siemens-supported OS and that STEP 7 has not yet been installed. Order matters: install the RTX kernel and COM 723 before STEP 7 so that STEP 7's hardware catalog recognizes the slot PLC PG/PC interface.

Step 1 — Verify Host Hardware

1. Power down the host PC.
2. Open the chassis and confirm the WF723A is fully seated in the PCI/PC-104 slot.
3. Power on and enter the BIOS; confirm the PCI slot is enabled and no resources are conflicting (no legacy ISA resources mapping over the PCI memory window).
4. Boot Windows and verify the module appears in Device Manager under an appropriate category (Siemens AG / SIMATIC slot PLC).

Step 2 — Install COM 723

1. Insert the COM 723 installation media or mount the ISO.
2. Run Setup.exe as Administrator.
3. Accept the license agreement and provide the license key when prompted. The wizard transfers the key to the slot PLC's license memory during the first connection.
4. Select the installation directory; the default C:\Program Files\Siemens\COM723 is recommended.
5. Choose Typical Install for a single-host commissioning workstation, or Custom to omit the RTX diagnostic console on production cells.
6. Reboot when prompted. The Venturcom RTX subsystem starts as a Windows service.

Step 3 — Install STEP 7

1. Install STEP 7 V5.x after the COM 723 reboot.
2. In the PG/PC interface selection, choose S7ONLINE (STEP 7) -> PC internal (local) for project download to the slot PLC via the RTX-named pipe, or select the CP5611/CP5512 PROFIBUS interface for direct DP download.
3. Verify the slot PLC appears in Accessible Nodes by opening Start > SIMATIC > STEP 7 > Accessible Nodes.

Step 4 — Initial COM 723 Configuration

1. Launch COM 723.
2. Select the slot PLC from the discovered devices list. The firmware version, hardware revision, and license status are displayed.
3. Open RTX Configuration and set the real-time scheduler tick. The default (1 ms) is appropriate for S7-300-class scan times. Do not change the tick without a documented performance justification.
4. Set the slot PLC's PROFIBUS DP address (default 2).
5. Save the configuration. COM 723 prompts for a restart of the RTX subsystem; accept.

Step 5 — Verification

After the RTX restart, re-open COM 723 and confirm the slot PLC reports RUN. If the status is STOP with a fault, refer to the Diagnostics section.

6. Commissioning the WF723A Slot PLC

Commissioning is the transition from a freshly flashed slot PLC to a node executing user logic. The workflow is similar to an S7-300 CPU but with the host PC and RTX subsystem added to the failure surface.

6.1 Memory Reset and Firmware Update

From COM 723:

1. Select Slot PLC > Memory Reset. This clears work memory, retentive flags, and the diagnostic buffer.
2. To update firmware, select Slot PLC > Firmware Update and browse to the .upd or .bin file matching the module variant. Do not interrupt power during the update.
3. After the update completes, perform another memory reset to clear any state carried over from the previous firmware.

6.2 STEP 7 Project Structure

Create the STEP 7 project as for any S7-300 station:

1. Insert a SIMATIC 300 station.
2. In the hardware catalog, expand SIMATIC 300 > CPU 300 > CPU 315-2 DP (or the specific CPU proxy the WF723A variant exposes).
3. Drag the proxy into the rack. The slot PLC's PROFIBUS master interface appears at IF1.
4. Configure the PROFIBUS subnet (baud rate, bus parameters, station addresses for slaves).
5. Assign the slot PLC as DP master and configure slaves' I/O address ranges.
6. Write OB1 and any required FBs/FCs/DBs.

6.3 Downloading the Project

1. In STEP 7, select PLC > Download to Target.
2. Choose the target PG/PC interface (named pipe or PROFIBUS CP).
3. Confirm. STEP 7 transfers the hardware configuration and blocks to the slot PLC via the RTX host channel.
4. Switch the slot PLC to RUN using PLC > Operating Mode or by setting the mode selector on the module faceplate to RUN.

6.4 Backup Image Creation

After a successful download, return to COM 723 and create a backup image:

1. Select Backup > Create.
2. Specify the destination path on the host. The image includes the slot PLC firmware, RTX configuration, license reference, and a snapshot of the STEP 7 project stored on the module.
3. Label the image with the project name and revision.
4. Store the image on a network share or removable media in addition to the host PC.

7. STEP 7 Project Integration and OPC Connectivity

The WF723A appears to STEP 7 as a CPU 315-2 DP. Standard S7 programming tools apply. The host PC gains additional connectivity:

7.1 Host-to-Controller Channels

7.2 Recommended Tag Cycle Times

When bridging STEP 7 tags to a WinCC HMI running on the same host, configure the OPC server tag update rate conservatively:

• Process values: 250 – 500 ms
• Alarms: 100 ms
• Diagnostics: 1000 ms

Setting the OPC rate below the slot PLC scan time produces false repeat values and wastes bus bandwidth.

8. PROFIBUS DP Network Configuration

The WF723A is a class-1 PROFIBUS DP master. It can address up to 124 slaves on a single segment, limited by repeaters and bus length. Use STEP 7's HW Config to build the DP master system.

8.1 Baud Rate vs. Segment Length

8.2 Termination and Shielding

Always terminate the bus at both physical ends with the PROFIBUS connector's built-in terminating resistor (switch position ON). The shield must be clamped to the connector's shield clamp and bonded to a low-impedance ground at one point of the segment to avoid ground loops. Failure to terminate is the single most common cause of intermittent Station Failure diagnostics.

8.3 Diagnostic Repeaters

For segments longer than the table values or where reflection problems persist, install a diagnostic repeater (e.g., Siemens 6ES7972-0AB01). The repeater reports per-segment signal quality, allowing localized isolation of cable damage without taking the bus offline.

9. Diagnostics, Error Codes, and Troubleshooting

Diagnosing a WinAC slot PLC requires examining four information sources in this order:

1. The slot PLC's mode LED (STOP / RUN / FRCE / BUSF).
2. COM 723's diagnostic buffer (last 50 events).
3. STEP 7's online PLC > Module Information (CPU fault buffer, I/O status).
4. The RTX subsystem's boot log (via COM 723 > RTX > View Log).

9.1 LED States

9.2 Common CPU Fault Codes (S7 Diagnostic Buffer)

9.3 Common Installation Pitfalls

• Symptom: Slot PLC not visible in Accessible Nodes.
  Cause: RTX service not running or wrong PG/PC interface selected.
  Fix: Open Control Panel > SET PG/PC Interface, choose the RTX-named-pipe interface, restart the RTX service.
• Symptom: Download starts then aborts with Online: Connection to PLC broken.
  Cause: Firewall or anti-virus blocking the S7ONLINE named pipe.
  Fix: Whitelist S7WGCOM.exe and the RTX port range. Disable Windows firewall temporarily for diagnosis, then re-enable with the correct rule.
• Symptom: Slot PLC enters STOP after each power cycle.
  Cause: Corrupted firmware or missing license.
  Fix: Restore from backup image via COM 723; re-apply license if needed.
• Symptom: BUSF LED solid after HW Config download.
  Cause: PROFIBUS baud rate or address mismatch between master and slaves.
  Fix: Verify each slave's address and the bus profile in HW Config.
• Symptom: Slot PLC runs but scan time degrades over hours.
  Cause: RTX scheduler starvation by a runaway Windows process.
  Fix: Use Process Explorer to identify high-CPU processes; exclude engineering tools from real-time priority.

9.4 Field-Proven Diagnostic Sequence

1. Capture LED state.
2. Read COM 723 diagnostic buffer (most recent 20 events).
3. Open STEP 7 PLC > Module Information > Diagnostic Buffer.
4. Confirm OB1 is being called (statistical counter in OB1).
5. If the bus is the suspect, use a PROFIBUS diagnostic tool (e.g., Siemens BT 200 or Amprolyzer) to capture the bus trace.
6. Document the fault, the recovery action, and the firmware/STEP 7 versions in the maintenance log.

10. Migration Paths to Modern Controllers

The WF723A belongs to a product generation that has been superseded. Sites still running it should plan a migration window before spare parts and Siemens support contracts expire. Three viable migration paths exist:

10.1 Migration to WinAC RTX Software Controller

Siemens' WinAC RTX (Software Controller, e.g., 6ES7671-0RC0x-xxx0) moves the real-time runtime back into the host OS, using the RTX hypervisor. This eliminates the slot PLC hardware but retains the S7-300-compatible programming model. The STEP 7 project can be migrated with minimal changes; the hardware catalog entry changes from CPU 315-2 DP to the WinAC RTX entry.

10.2 Migration to SIMATIC Open Controller

The SIMATIC Open Controller (e.g., 6ES7677-1DDxx-xxx0) is an ET 200SP-based PC controller with a S7-1500 CPU and a Windows runtime running on the same device. This path requires project conversion to TIA Portal and a S7-300-to-S7-1500 migration. It is the most future-proof option but requires significant engineering effort.

10.3 Migration to ET 200SP CPU or S7-1500 Standalone

For sites that no longer require PC-based integration, an ET 200SP CPU or S7-1500 standalone provides equivalent control with modern tooling. PROFIBUS DP can be retained with PROFINET/DP coupling, or migrated to PROFINET entirely.

10.4 Migration Checklist

1. Inventory all WF723A stations: order number, firmware, STEP 7 project version, peripheral I/O.
2. Confirm the destination controller's compatibility list (TIA Portal version, hardware catalog entry).
3. Convert the STEP 7 V5.x project using the TIA Portal migration tool. Address any unsupported S7-300 instructions.
4. Plan a parallel-run window with the existing controller.
5. Update the maintenance plan and operator documentation.

11. Safety, Compliance, and Operational Notes

• The WF723A is a standard (non-failsafe) controller. It cannot host F-programs (F-CPU functionality) on its own; safety functions require a separate F-CPU or F-I/O with PROFIsafe.
• The host PC must be protected against unauthorized USB and network access. A compromised host can issue writes to the slot PLC; rely on STEP 7 password protection and access control on the WinCC layer.
• Always perform a controlled shutdown of the RTX subsystem before powering off the host PC. Abrupt power loss can corrupt the slot PLC firmware and require a backup-image restore.
• Schedule a quarterly image-backup and an annual firmware-revision review.
• Keep the COM 723 installation media in a documented location; the backup-image restore depends on a working COM 723 install on the host.

12. Frequently Asked Questions