Overview
Showing up to a Modbus commissioning job without the right tools wastes time and money. This checklist covers the physical tools, adapters, cables, and software you should carry to site for both Modbus RTU (serial) and Modbus TCP (Ethernet) work.
This complements the Modbus RTU Pre-Commissioning Checklist, which covers the verification steps to perform before going to site. This article covers the gear to bring with you.
[!TIP] Build a dedicated commissioning kit bag that stays packed between jobs. Restock consumables (resistors, cable ties) after each site visit.
Serial Communication Tools
These are essential for Modbus RTU and RS-232/RS-485 work.
USB-to-RS-485 Converter
Required for connecting a laptop to an RS-485 bus. The converter provides the differential signaling needed for Modbus RTU communication.
- Look for converters with switchable termination (120 Ω built-in)
- Ensure the converter supports the baud rates you’ll need (9600, 19200, 38400, 115200)
- Carry the correct driver pre-installed on your laptop — see How to Install the Driver for the Abacus USB to RS232/485 Converter
[!NOTE] Not all USB-to-RS-485 converters handle line driver turn-on/off timing correctly. Cheap converters can cause the last byte of a response to be clipped. Invest in a quality converter.
USB-to-RS-232 Converter
Required for devices with DB9/DB25 serial ports. Less common than RS-485 on modern installations, but still found on legacy equipment and some building controllers.
Serial Breakout Box
A breakout box exposes individual RS-232 signal lines (TXD, RXD, RTS, CTS, DTR, DSR) on LEDs or test points. Invaluable for:
- Verifying which pins are active
- Diagnosing handshaking issues
- Confirming TX/RX pin assignments
Null Modem Adapter (TX/RX Crossover)
Swaps pins 2 and 3 on a DB9 connection. If you connect two DTE devices (e.g., laptop to controller) and get no communication, the TX/RX lines may need crossing.
Carry a small inline adapter rather than re-wiring cables on site.
DB9 Terminal Block Adapters
Male and female DB9-to-screw-terminal adapters let you connect bare wires to DB9 ports without soldering. Essential for making up cables on site.
DB9/DB25 Connector Kits
Solder-free make-up kits with DB9 and DB25 shells, pins, and hoods. For building custom serial cables when the supplied cables don’t match.
Gender Changers
Male-to-male and female-to-female DB9 gender changers. You will eventually encounter two cables that are both the wrong gender.
RS-485 Bus Components
Termination Resistors
Carry an assortment of resistors for RS-485 bus termination:
| Resistance (Ω) | Use |
|---|---|
| 120 | Standard termination (matches most cable impedance) |
| 100 | Alternative for some cable types |
| 150 | Alternative for higher-impedance cable |
| 52.3 | Strong pull-down for biasing networks |
| 75 | Used on some legacy installations |
0.25 W (¼ watt) resistors are sufficient for most Modbus installations.
[!TIP] Pre-solder resistors onto short jumper wires with alligator clips for quick temporary installation during commissioning. You can replace with permanent resistors after confirming the bus works.
Extra Wire
Bring a spool of shielded twisted pair cable (e.g., Belden 3105A or 9841) for making up short jumper runs or replacing damaged segments. See the RS-485 Physical Layer Reference for cable specifications.
Ethernet / Modbus TCP Tools
Ethernet Patch Cables
Carry at least 3–4 cables of varying lengths (1m, 3m, 5m). Both straight-through and crossover if you may encounter older equipment without auto-MDIX.
Network Hub (Not a Switch)
A true Ethernet hub is critical for Wireshark packet capture. A standard switch will NOT show you traffic between other devices.
| Device | Works for Packet Capture? |
|---|---|
| Hub | ✅ Yes — mirrors all traffic to all ports |
| Managed switch with port mirroring | ✅ Yes — configure a monitor port |
| Unmanaged switch | ❌ No — only shows broadcast traffic |
| Router | ❌ No |
[!WARNING] Many devices labeled “hub” are actually switches. If the product description mentions “full-duplex” or “learning mode,” it’s a switch. Look for an explicit 10 Mbps hub or a managed switch with a dedicated monitor port.
Recommended Hubs
- 10 Mbps networks: DX-EHB4 4-Port 10 Mbps Hub, D-Link DE-805TP
- Mixed-speed networks: Netgear DS104 Dual Speed Hub
Software
Pre-install these tools on your laptop before going to site. Don’t rely on downloading at a site with limited or no internet.
Wireshark
Free, open-source packet analyzer. Essential for Modbus TCP troubleshooting.
Download: wireshark.org
CAS Modbus Scanner
Chipkin’s free Modbus diagnostic utility. Reads coils, discrete inputs, holding registers, and input registers from any Modbus device. Displays values in Binary, Hex, UINT16, INT16, UINT32, INT32, and Float32 formats.
- Supports both serial (RTU) and Ethernet (TCP) connections
- Multiple connections, devices, and requests in one session
- Auto-update polling for continuous monitoring
Download: chipkin.com/cas-modbus-scanner
CAS Modbus RTU Parser
Analyzes raw Modbus RTU message bytes and decodes them: function code, register addresses, data, CRC validation, and error detection.
Download: chipkin.com/cas-modbus-rtu-parser
Terminal Emulator
A serial terminal program (PuTTY, Tera Term, or similar) for raw serial communication testing and device console access.
Packing Checklist
Print this checklist or save it to your phone:
Serial Tools
- USB-to-RS-485 converter (with drivers installed)
- USB-to-RS-232 converter (with drivers installed)
- Serial breakout box
- Null modem adapter (TX/RX crossover)
- DB9 terminal block adapters (male + female)
- DB9/DB25 make-up kits (solder-free)
- Gender changers (M-M and F-F)
RS-485 Components
- Termination resistors (52.3 Ω, 75 Ω, 100 Ω, 120 Ω, 150 Ω)
- Shielded twisted pair cable (spare spool)
- Wire strippers and screwdriver set
Ethernet Tools
- Ethernet patch cables (3–4, various lengths)
- Network hub or managed switch with mirror port
- Crossover Ethernet cable (for legacy devices)
Software (Pre-Installed)
- Wireshark
- CAS Modbus Scanner
- CAS Modbus RTU Parser
- USB serial drivers
General
- Laptop (charged, with all software installed)
- Power strip / extension cord
- Cable ties and labels
- Multimeter
- Camera / phone for documenting wiring
Related Articles
- Modbus RTU Pre-Commissioning Checklist — verification steps to perform before going to site
- RS-485 Physical Layer Wiring & Termination Reference — cable specs, termination, and biasing
- How to Install the Driver for the Abacus USB Converter — USB serial driver installation
- Wireshark for Modbus TCP — packet capture and analysis guide
- Modbus Device Discovery & Network Scanning Guide — finding devices on the bus
- Modbus Troubleshooting Guide — systematic diagnosis workflow
Chipkin Can Help
Need a commissioning kit recommendation or on-site support? Chipkin support can help configure your QuickServer gateway before you arrive at site, minimizing on-site troubleshooting time.