Fixing C-more Micro EA1-S3ML PLC COM Time Out on BRX

Problem Details

A C-more Micro EA1-S3ML panel connected to a BRX BX-DM1E-M-D CPU through a POM (Pluggable Option Module) serial port reports PLC COM time out on the panel screen. Nothing appears on the tag display; the error persists after power cycling both devices and after confirming firmware is current.

"PLC COM time out" is generic: the panel transmitted a Do-more protocol request and never received a valid, complete response inside the panel's timeout window. It does not distinguish between wrong wiring, wrong protocol, wrong node address, and wrong serial framing. The failure is on the physical/serial-framing layer or the addressing layer, not in the tag database.

Root Cause

In this case the fault was a baud rate mismatch between the Do-more POM port and the C-more Micro project's PLC port configuration. The Do-more port had been configured at a rate the panel driver does not offer — 115200 baud is not selectable in the C-more Micro panel manager for the Do-more serial driver. With the PLC transmitting at one rate and the panel sampling at another, the panel sees framing/parity garbage or nothing at all, discards it, and expires its response timer.

The diagnostic trap: the technician verified the settings on the panel's own setup screen but never opened the PLC communication dialog inside the C-more Micro programming software, where the project-stored baud rate lives. Correcting the rate there and re-downloading the project restored communication immediately.

Failure modes that produce the same message

Solution

1. Read the actual PLC port settings. In Do-more Designer, connect to the BX-DM1E-M-D over its Ethernet port (this keeps you online while you change the serial port) and open the CPU/system configuration for the POM slot. Record protocol mode, baud rate, data bits, parity, stop bits, and node/station address exactly as configured.
2. Confirm the POM port is in Do-more protocol mode. The port must be serving the Do-more (K-sequence-class) protocol the panel's Do-more driver speaks, not Modbus RTU, not ASCII in/out, not a custom protocol owned by ladder logic. If any ladder instruction has claimed the port, the panel will never get a reply.
3. Open the project-level PLC settings in the C-more Micro programming software. Go to the panel/PLC communication configuration in the project — not the on-panel setup screen. Verify the driver is the AutomationDirect Do-more selection and inspect the baud dropdown.
4. Pick a baud rate that exists in both lists. If the PLC is set to a rate absent from the panel dropdown (115200 in this case), change the PLC side down to a rate the panel offers. Then set data bits, parity, and stop bits identically on both ends. Note the value you choose — every later step depends on both sides agreeing.
5. Match the node/station address. Whatever address the POM port is configured with must be entered as the PLC address in the C-more Micro project.
6. Download both. Write the corrected port configuration to the BRX CPU, then download the corrected C-more Micro project to the panel. A settings change that is not downloaded has no effect at runtime.
7. Power cycle the panel so it renegotiates the link with the new framing.

Wiring checks before you chase software

• Verify the POM installed is the correct electrical standard for your cable: RS-232 POM for a 3-wire TXD/RXD/GND run, RS-485 POM for a differential pair. A cable built for one will not work on the other.
• RS-232: PLC TXD must land on panel RXD and PLC RXD on panel TXD, with signal ground bonded end to end. Keep the run short and away from VFD motor leads.
• RS-485: keep polarity consistent (+ to +, − to −), use shielded twisted pair, ground the shield at one end only, and terminate the ends of the segment.
• Confirm the panel is powered from a supply whose 0 V reference does not float relative to the PLC's, especially on RS-232.

Verification

1. Serial activity LEDs. Watch the POM/port TX and RX indicators on the BRX. RX blinking with no TX means the PLC is receiving bytes but rejecting them — framing, protocol, or node address is still wrong. Neither blinking means the panel is not transmitting or the cable is dead.
2. Panel error banner clears. The "PLC COM time out" message should disappear within a few poll cycles after power-up, not flicker on and off. Intermittent reappearance points to marginal signal quality (noise, long RS-485 run, missing termination) rather than configuration.
3. Live data test. Place a numeric display object bound to a known Do-more memory location on the panel, force that value from Do-more Designer's data view, and confirm the panel tracks the change.
4. Write test. Add a momentary pushbutton object writing to a bit and confirm the bit toggles in Do-more Designer. Read-only success with failed writes usually indicates a memory-protection or address-range issue, not a comms issue.
5. Soak test. Leave the panel running 15–30 minutes with machine power applied and drives running. Time outs that only appear when a VFD starts are an EMC/grounding problem: re-route the cable, improve shield grounding, or drop to a lower baud rate for margin.

Documentation to update after the fix

Prevention

• Standardize one serial rate and framing across all HMI-to-PLC serial links in the plant, chosen from the rates the most limited device supports. Never configure a PLC port to a rate the HMI driver cannot select.
• Treat the panel's on-screen setup menu as a diagnostic view only. Make all changes in the project and download.
• When a BRX CPU has an Ethernet port available, keep it wired for programming access. Debugging a broken serial link while your only path to the CPU is that same serial link wastes time.
• Label the POM slot with its protocol, baud, and node address on the panel door drawing.

FAQ