Simply Modbus Slave

Simply Modbus Slave 101 is a software test tool for Windows PCs that simulates a Modbus RTU or Modbus ASCII slave device. It acts like a “soft PLC,” letting engineers test, troubleshoot, and monitor Modbus serial communications in real time without needing physical hardware.

The tool works by watching a serial port on your computer for request messages from a Modbus Master. Once it sees a valid request, it reads data from its internal data tables to build and send a reply back to the master. Key Features

Dual Protocol Support: It simulates both Modbus RTU (binary encoding) and Modbus ASCII (text encoding) communication modes.

Real-Time Monitoring: It displays data traffic on the serial port as it happens, making it easy to watch the master-slave dialogue.

Standard Function Codes: It supports common Modbus commands including FC 01, 02, 03, 04, 05, 06, 15, and 16 for reading and writing data.

Configuration Files: You can save and load your specific table setups and register environments for quick testing later on. How the Software Operates

Request Capture: The software continuously polls the specified computer COM port.

Validation: When a message arrives, it verifies the Slave ID and checks that the requested data addresses exist within its configured data tables.

Response Generation: If everything matches, it instantly replies to the master with the relevant data. Demo vs. Licensed Versions

The software can be evaluated for free, but it has specific operational limits until unlocked:

Demo Mode: The program offers full configuration and testing functionality, but it restricts communication by limiting the number of response messages to six per session. Once the limit is reached, you must restart the program to send more messages.

Full Version: Entering a valid license key bypasses the 15-second “Loading Demo” window and unlocks unlimited, continuous message transmissions.

You can download the program directly or access documentation from the official ⁠Simply Modbus Slave Page. If you are setting up a test environment, let me know: What Modbus Master software or hardware are you using?

Do you need help understanding the register mapping or specific function codes?

Are you connecting via physical RS-232/RS-485 wires or using a virtual COM port? Simply Modbus Modbus Test Tools – TCP Client, RTU/ASCII Master & Slave