QModMaster vs Simply Modbus: Honest Comparison
Simply Modbus (simplymodbus.ca) is best known for its Modbus tutorials and lightweight test tools — an RTU Master tool and a Slave Simulator. QModMaster is a free, open source Modbus master. They overlap less than you’d think — here is the honest breakdown.
Feature Comparison
| Feature | QModMaster | Simply Modbus Tools |
|---|---|---|
| License & Price | LGPLv3 — free, no demo limits | Commercial — free download runs in demonstration mode until licensed (per vendor) |
| Platforms | Windows 7/10/11, Linux | Windows (per vendor) |
| Master Protocols | Modbus RTU + TCP | Modbus RTU/ASCII (per vendor) |
| Slave Simulator | No — master only | Yes — Slave Simulator tool (per vendor) |
| Bus Monitor | Built-in raw-hex bus monitor | Not advertised — check vendor docs |
| Learning Resources | Tutorial + user manual on this site | Extensive free Modbus tutorials on simplymodbus.ca (per vendor) |
| Support | Community only — no official tech support | Vendor (per site) |
Where QModMaster Wins
- Actually free: LGPLv3 with no demonstration mode, no licensing step, no expiry.
- Modbus TCP support — the Simply Modbus master tool is RTU/ASCII; QModMaster covers Ethernet devices too.
- Raw-hex bus monitor and Linux builds for serious debugging on any bench.
Where Simply Modbus Earns a Look
- Excellent free Modbus tutorials — one of the best places on the web to learn how the protocol actually works.
- Slave Simulator included: simulate a slave device to test your PLC or master application — QModMaster is master-only and can’t do this.
- ASCII mode and try-before-you-buy demo, handy for legacy ASCII-only equipment.
Frequently Asked Questions
Is Simply Modbus software free?
No — per the vendor, the free download “has full functionality and runs in demonstration mode until licensed.” QModMaster is free under the LGPLv3 with no demo restrictions or licensing step.
Does the Simply Modbus master tool support Modbus TCP?
The vendor describes it as a “Modbus RTU/ASCII Master Tool” — check their docs for current TCP support. QModMaster supports both Modbus RTU and Modbus TCP.
Can QModMaster act as a slave like the Simply Modbus Slave Simulator?
No — QModMaster is a master (client) simulator only. If you need to simulate a slave device to test a PLC or master application, the Simply Modbus Slave Simulator is the relevant tool.
Where should a complete beginner start?
Learn the protocol with the free tutorials on simplymodbus.ca, then get hands-on with QModMaster — free, portable, and this site walks you through your first session step by step.