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Modbus/TCP Connectivity Guide

Overview​

What is Modbus/TCP?​

Modbus/TCP is an industrial communication protocol that runs over standard Ethernet networks. It's one of the most widely adopted protocols for connecting PLCs, industrial equipment, and automation systems.

When to Use Modbus/TCP:

  • Equipment has Modbus/TCP server capability
  • PLCs (Allen Bradley, Siemens, Click, etc.)
  • Industrial controllers and automation equipment
  • I/O modules (Sealevel, WISE, etc.)
  • Third-party gateways (Kepware, MatrikonOPC)

Key Characteristics:

  • Standard TCP/IP networking
  • Default port: 502
  • Function codes for different data types
  • Unit ID for device addressing
  • Widely supported by industrial equipment

Compatible Equipment​

PLCs:

  • Click PLCs (Ethernet models: C0-10DRE-D, C0-11DD2E-D, etc.)
  • Allen Bradley CompactLogix / ControlLogix (via EtherNet/IP adapter)
  • Siemens S7 PLCs
  • Many others with Ethernet capability

I/O Modules:

  • Sealevel eI/O series (170E, 130E, etc.)
  • Advantech WISE-4000 series
  • Third-party Modbus I/O modules

Gateways:

  • Kepware servers
  • MatrikonOPC
  • Protocol converters

Industrial Equipment:

  • Some CNC controls
  • VFDs (variable frequency drives)
  • Process controllers
  • Automation equipment

Prerequisites​

  • Device with Modbus/TCP server capability
  • Modbus register map or tag list from manufacturer
  • Device IP address and port (typically 502)
  • Network access between device and Edge
  • MachineMetrics Edge device deployed

Physical Connection​

Step 1: Connect Ethernet

  • Plug CAT5/CAT6 cable into device
  • Connect to network switch
  • Ensure Edge device is on same network

Step 2: Configure Static IP

  • Set static IP on device (recommended)
  • Document IP address
  • Typical port: 502

Step 3: Test Connectivity

  • Ping device IP from Edge or computer
  • Verify firewall allows TCP port 502

Modbus Addressing​

Address Spaces​

Modbus has different function codes and address ranges:

Function Code 1 - Read Coils (digital outputs/internal coils)

  • Addresses: 1-9999 or 00001-09999
  • Use for reading output states

Function Code 2 - Read Discrete Inputs (digital inputs)

  • Addresses: 10001-19999
  • Use for reading input states (most common for I/O modules)

Function Code 3 - Read Holding Registers (read/write registers)

  • Addresses: 40001-49999

Function Code 4 - Read Input Registers (read-only registers)

  • Addresses: 30001-39999

Address Conversion​

5-Digit Addresses:

  • Use as-is in script
  • Example: Address 40005 → address: 40005

6-Digit Addresses:

  • Drop leading digit and subtract 1
  • Example: 400010 → drop 4, subtract 1 → 9
  • Example: 300020 → drop 3, subtract 1 → 19

Configuration Parameters​

unit-id: 1                   # Device ID (1-247)
byte-order: big              # Big or little endian
word-order: big              # For 32-bit values
address-space: mixed         # or function3 or extended

Address Space Options:

  • mixed: Uses 40001, 30001, etc. format (most common)
  • function3: All registers assumed to be holding registers
  • extended: For 6-digit addresses

Configuration Examples​

Example 1: Generic PLC​

Device: Click PLC or similar

  • Coil 1: Machine running status
  • Register 40001: Part counter (int16)

Adapter Script:

version: 2
unit-id: 1
address-space: mixed

coils:
  machine-running:
    address: 1
    func: 2        # Use func 2 for digital inputs

registers:
  counter:
    address: 40001
    type: int16
    func: 3

variables:
  execution:
    - source: machine-running
    - state:
        - ACTIVE: this
        - READY: true
  
  part-count:
    - source: counter
    - value-increase
    - count

data-items:
  - execution
  - part-count

Example 2: PLC with Multiple Signals​

Device: PLC with green lamp, red lamp, and counter

  • Coil 1: Green lamp (running)
  • Coil 2: Red lamp (alarm)
  • Register 40001: Part counter

Adapter Script:

version: 2
unit-id: 1

coils:
  green-lamp:
    address: 1
    func: 2        # Read Discrete Inputs
  red-lamp:
    address: 2
    func: 2

registers:
  counter:
    address: 40001
    type: int16

variables:
  execution:
    - state:
        - INTERRUPTED: red-lamp
        - ACTIVE: green-lamp
        - READY: true
  
  part-count:
    - source: counter
    - value-increase
    - count

data-items:
  - execution
  - part-count

Adding Machine in MachineMetrics​

Step 1: Assets → Machines → Add Machine

Step 2: Enter machine details (name, make, model)

Step 3: Select adapter type:

  • Modbus TCP (for PLCs, generic Modbus devices)
  • Digital IO (Sealevel 170E) (for Sealevel eI/O)
  • Digital IO (WISE-4050) (for WISE modules)

Step 4: Enter configuration:

  • IP Address: Device IP
  • Port: 502 (or custom)
  • Adapter Script: Paste YAML configuration

Step 5: Test connection and save

Troubleshooting​

Connection Issues:

  • Verify IP address and port
  • Check firewall allows TCP port 502
  • Ping device from Edge

Data Not Appearing:

  • Verify register addresses in script match device map
  • Check function codes (1, 3, 4)
  • Verify data types (int16, int16, uint32, float32)

Address Errors:

  • Confirm 5-digit vs 6-digit addressing
  • Apply correct conversion if needed

Additional Resources​

Questions? Contact support@machinemetrics.com