GE Fanuc 90-30 PLC Slot 3 IC693CMM311 Timeout Fault Fix

GE Fanuc Series 90-30 PLC Fault: Option Module Software Timeout on Slot 3 IC693CMM311

A GE Fanuc Series 90-30 PLC recently recorded a critical fault in its CPU fault table. The diagnostic message reads “Option Module Software Timeout.” As a result, the fault points directly to slot 3 in the main rack. The installed module in that physical location is an IC693CMM311 Communications Coprocessor Module. According to the system reference manual, this specific fault belongs to the “Option Module Software Failure” group. Moreover, the Series 90-30 architecture classifies these failures as fatal events.

Understanding the IC693CMM311 and Its Role in Industrial Automation

The IC693CMM311 acts as a high-performance coprocessor for modular Series 90-30 CPUs. In addition, this module supports multiple industrial protocols, including CCM, RTU (Modbus slave), and SNP. It features two serial ports: Port 1 handles RS-232 applications, while Port 2 supports either RS-232 or RS-485. In many legacy installations, this CMM module manages critical HMI links or PLC-to-PLC data exchange. Consequently, a timeout fault in this module can disrupt supervisory control and data acquisition functions across the factory automation network.

Root Cause Analysis of the Software Timeout Fault

The “Option Module Software Timeout” error typically occurs when the CPU cannot complete a communication handshake with the option module. During each PLC sweep, the CPU services communications windows for intelligent modules. If the CMM311 fails to respond within the allocated time slot, the CPU flags this fault. Therefore, the timeout suggests either a module firmware hang or a CPU sweep overload. In some documented cases, excessive COMMREQ instructions can overload the module’s processing capacity. Additionally, a corrupted configuration block or a failing hardware component inside the CMM311 can trigger this fatal fault.

Temporary Mitigation via CPU Sweep Limit Adjustment

Increasing the CPU sweep timeout limit provides a temporary workaround for this communication timeout. The Series 90-30 CPU supports a “Constant Sweep Time” mode, which allows engineers to define a fixed sweep duration. For CPUs 311 through 341, the configurable range spans 5 to 200 milliseconds. However, engineers must set this value at least 10 milliseconds higher than the normal sweep time displayed in the status line. This adjustment prevents extraneous oversweep faults while giving the CMM311 additional time to complete its software routines. Nevertheless, this action merely masks the underlying issue and does not resolve the root hardware or firmware failure.

Step-by-Step Configuration Procedure for the Sweep Limit

To implement this temporary fix, connect the programming workstation to the PLC. Then, open the Logicmaster 90 or Proficy Machine Edition configuration software. Navigate to the CPU configuration screen and locate the Sweep Mode and Sweep Timer parameters. Select “Constant Sweep Time” from the available sweep modes. After that, enter a new sweep timer value that exceeds the current normal sweep time by 10 to 20 milliseconds. Finally, store the configuration from the programmer to the PLC while the processor is in STOP mode. Once stored, this becomes the default sweep mode for subsequent RUN cycles.

Limitations and Risks of the Sweep Limit Workaround

Although increasing the sweep limit can temporarily restore system stability, this approach carries inherent risks. If the constant sweep timer expires before the sweep completes, the CPU logs an oversweep fault at the beginning of the next scan. Moreover, extending the sweep time affects the deterministic response of the entire control system. For instance, the delay between output updates and subsequent input scans grows proportionally. Consequently, time-critical control loops may experience degraded performance. Additionally, the fundamental timeout issue within the CMM311 remains unaddressed. Therefore, this workaround serves only as a short-term measure until a proper repair or replacement occurs.

Recommended Long-Term Solutions and Hardware Actions

For a permanent resolution, engineers should investigate the CMM311 module directly. First, verify that the module’s Restart/Reset pushbutton functions properly when the MODULE OK LED is on. Second, inspect the serial port cabling and the IC693CBL305 Wye cable for physical damage or loose connections. Third, check the COMMREQ logic in the application program for excessive frequency or invalid parameters. If the fault persists, replace the IC693CMM311 with a known-good spare unit. Finally, consider migrating the communication function to a modern platform if the legacy hardware reaches end-of-life status.

Key Technical Summary for Field Engineers

Application Case and Solution Scenario

Consider a factory automation line where a Series 90-30 CPU controls multiple remote I/O drops. The IC693CMM311 in slot 3 handles Modbus RTU communication to a supervisory DCS. If this module times out, the DCS loses visibility of the production line. In this scenario, increasing the sweep limit may restore communication for a few hours. However, the best practice is to replace the CMM311 and verify all COMMREQ logic. This approach minimizes unplanned downtime and protects the control system from further faults.

Frequently Asked Questions

1. What does “Option Module Software Timeout” mean on a GE Fanuc Series 90-30 PLC?
This fault means the CPU could not complete a communication handshake with an intelligent option module, such as the IC693CMM311, within the allocated sweep window.

2. Can I clear this fault by increasing the CPU sweep limit?
Yes, increasing the constant sweep time can temporarily clear the fault. However, it does not fix the root cause inside the CMM311 module.

3. What is the recommended sweep timer value for CPUs 311 through 341?
The configurable range is 5 to 200 milliseconds. Engineers should set the value at least 10 milliseconds above the normal sweep time.

4. When should I replace the IC693CMM311 module?
Replace the module if the fault persists after checking cabling, COMMREQ logic, and the Restart/Reset pushbutton. A known-good spare unit is the best long-term solution.

5. Does this fault affect other parts of the control system?
Yes. Because the fault is fatal, it can disrupt HMI links, PLC-to-PLC data exchange, and supervisory control and data acquisition functions.