Mod_RSSim is a Modbus RS-232 (RTU) and TCP/IP Slaves and Allen Bradley DF1 simulator.
Allen-Bradley is a trademark of Rockwell Corporation USA; MODBUS of Modicon USA; JOY is a trademark of Joy Mining Machinery UK; Windows is a trademark of Microsoft Corporation USA.
There are two modifications of the utility:
ModRSSim - the initial project, which is no longer supported by the developer. The project home page is
ModRSSim2 - continuation of the ModRSSim project by a different developer. This project is developed and supported. The project home page is
https://sourceforge.net/projects/modrssim2/
The delivery kit of Modbus Universal MasterOPC Server contains ModRSSim2. But operation principles of ModRSSim and ModRSSim2 are the same, therefore the initial ModRSSim page could be used to learn more about the product.
This simulator was originally designed to allow testing of MODBUS master devices, as such it also allows itself to use as a "virtual" PLC for training.
This simulator was written to allow the testing of a MODBUS RTU serial driver without having to get 255 little MODBUS PLCs into one office. It is not, by any means, a full implementation of the protocol; it implements only the common functions used in MODBUS and other protocols supported here.
It surpasses the limitations in other programs we have found in the past by:
Simulate more than one RTU at once. (Register values shared for all RTUs).
Allows editing and display of all the registers.
Allow scanning of registers not actually in the display.
Running more than 1 COM port (You have to run two copies of the program.). You need to run the first copy; then, when you run it again, it defaults to use the next free RS-232 port. All copies will use the same settings though.
A way of disabling just certain stations. (Just click on the boxes at the bottom.)
Load and save values you type into each register (the file is saved in the same folder) as well as simulate changes in the values. Hotkey <CTRL>-L = Load and <CTRL>-A for sAve.
You can specify the MODBUS PDU length (Protocol Data Unit) to simulate RTU’s with different internal telegram buffer sizes. Hotkey <CTRL>-M.
Display values in different formats (HEX/DEC etc.)
Specify responsiveness of the simulator to simulate slow hardware. Hotkey <CTRL>-S.
Simulate certain types of communication errors that would be hard to do in a "lab" situation.
A basic communication debugger showing request/response. Hotkey: <CTRL>-C.
Emulation to simulate MODBUS MOSCAD RTU on MODBUS. Hotkey <CTRL>-S or <CTRL>-M.
Simulate noisy communication lines. Hotkey <CTRL>-N.
It does check the CRC of all messages.
It does handle noisy comms properly.
Almost totally free, just mail the author for a key (or compile your own).
NOT supported
MODBUS ASCII protocol
This application is not intended as a full implementation of MODBUS RTU nor TCP/IP nor Allen-Bradley DF1, it is not commercially supported and no liability is held for any damage or application changes made as a result of its use.