Configuring C-more CM5 HMI Modbus TCP Communication with Python

Overview

The AutomationDirect C-more CM5 series (including the CM5-T7W 7-inch widescreen model) is a full-featured HMI platform with native Ethernet and serial drivers for more than 100 PLC families, plus Modbus TCP/IP, Modbus RTU, and BACnet. The panel's Tag Name Database separates Internal tags (HMI-only scratchpad registers) from Device tags (registers bound to an external controller address). This distinction is the root cause of the most common beginner error: attempting to write to an Internal tag from a remote client and receiving a No connection could be made because the target machine actively refused it reply from Python's pylogix library.

This tutorial walks through configuring the CM5 as a Modbus TCP client that polls a Python pyModbusTCP server on the host PC. After commissioning, the same pattern can be used to display any process value (barcode, lot number, scale weight, vision system result) on a Dynamic Text object without requiring a physical PLC.

Prerequisites

Reference: C-more Built-in Drivers overview (AutomationDirect video library) and the panel's User Manual / Installation Guide shipped with each unit.

Why pylogix Fails Against a CM5 Directly

pylogix speaks EtherNet/IP (CIP) and expects a Logix-family controller (CompactLogix, ControlLogix, MicroLogix 1100/1400) at the destination IP. The CM5 HMI does not run an EtherNet/IP server; its onboard protocols are listed in the table below.

When the Python script opens a TCP socket to the panel's IP on port 44818 (EtherNet/IP) or 2222 (CSP), nothing is listening, so the OS returns a connection refused error. The fix is to flip the relationship: make the panel the client and put a Modbus TCP server on the PC.

Step 1 — Configure Modbus TCP in Protocol Manager

1. Open the C-more project and select Setup → Protocol Manager (older firmware shows Panel Manager; both expose the same Modbus driver).
2. Click Add and choose Modbus TCP/IP Client from the driver list.
3. Assign the protocol to Port 1 (Ethernet) and configure the panel IP parameters: IP address, subnet mask, and gateway. The default IP 192.168.1.200 is acceptable for direct-to-PC links.
4. Click PLC Interface Configuration → Add. Set the IP Address field to the host PC's address (e.g., 192.168.1.24) and the Port to 502.
5. Set the Timeout to 1000 ms and the Retries to 3 during commissioning. Lower the timeout once the network is stable to speed up object redraws.
6. Click OK and download the project to the panel.

Step 2 — Build Modbus-Mapped Tags in the Tag Name Database

The Tag Name Database is accessed from the Project Navigator pane. For every value the HMI must display, create a row with the columns below.

Create a second tag to drive the visibility trigger:

• Tag Name: Usr_Show_TapeZone_Barcode
• Data Type: Boolean (mapped to a single coil or holding register bit)
• Address: 000001 (coil 0) or 400100 if you prefer holding registers

After these tags are committed, drop a Dynamic Text object on the screen, bind its Value Source to Usr_TapeZone_Barcode, and use the Visibility animation tied to Usr_Show_TapeZone_Barcode == 1.

Step 3 — Python pyModbusTCP Server

Install the package and run the example server. Port 502 is privileged on Linux; either run the script as root or rebind to 5020 and update the panel configuration to match.

# cm5_modbus_server.py
# Tested with pyModbusTCP 0.2.0, Python 3.10
from pyModbusTCP.server import ModbusServer
import time

server = ModbusServer("192.168.1.24", 502, no_block=True)

T1 = time.perf_counter()
bitValue = 0

try:
    print("Start server...")
    server.start()
    print("Server is online on 192.168.1.24:502")

    while True:
        T2 = time.perf_counter()
        if T2 - T1 >= 1.0:
            T1 = T2
            bitValue = 1 - bitValue
            print("Holding reg[0] ->", bitValue)
            # Holding register 0 maps to CM5 address 400001
            server.data_bank.set_holding_registers(0, [bitValue])
            # Optional: write a 4-char ASCII value to registers 10..11
            # 'A1B2' packed as two 16-bit words, low byte first
            server.data_bank.set_holding_registers(10, [0x3141, 0x3242])
except Exception as e:
    print("Server error:", e)
    server.stop()
    print("Server is offline")

String handling on Modbus requires packing two ASCII bytes per 16-bit register. For a 32-character barcode you must reserve 16 consecutive holding registers, then unpack in the panel by mapping each word to a substring of an ASCII String tag whose length is set to 32.

Step 4 — Wiring the Dynamic Text and Visibility

1. Insert a Dynamic Text object on the destination screen. Under Data, set the source to Usr_TapeZone_Barcode.
2. Open Animations → Visibility. Set the trigger condition to Usr_Show_TapeZone_Barcode == 1.
3. If you prefer a multi-state indicator, add a Multi-State Indicator whose states are sourced from the lookup text database. C-more's Message Database Data Logging workflow applies equally well for barcode events.
4. Compile and download the project. The panel will begin polling the Python server immediately on power-up.

Verification

Confirm the link end-to-end with these checks.

Troubleshooting Matrix

Performance and Limits

• The CM5 polls up to 32 Modbus tags per screen by default; additional tags may slow screen redraws.
• Recommended minimum poll period is 100 ms per tag; below this, the panel's internal queue saturates.
• String tags occupy 1 Modbus register per 2 ASCII characters plus 1 length register when using the panel's ASCII String type.
• Wire the host PC with a static IP (DHCP reservations fail-over) to avoid breaking the polling loop when leases expire.

FAQ