Modbus RTU 2 slaves simulator


Thread Starter

Vlad S.

Master PLC(s) controls two parts (Part 1 and Part 2) of field equipment via two serial RS232 cables using Modbus RTU protocol for each Part.

If operation of each Part doesn’t depend on condition of the other Part, it is easy to simulate communication with the Part using Modbus Slave software. Additionally OLE Automation together with VBA allows to create expected automatic responses from simulated equipment (for example, feedback signal about closed valve position after receiving from Master PLC a command to close the valve). This is a common way to simulate Modbus Slave with using Active X container.

However, in my case Part 1 and Part 2 of the equipment are interact with each other. Therefore, response from Part 1 to Master PLC depends on condition of Part 2 of the equipment and vice versa. In this situation the actual simulation of the both Parts 1 and 2 of the equipment can be created by different ways, for example:

1. Two Modbus Slave Simulators (for Part 1 and Part 2 of the equipment respectively) are installed on different PCs and they both have access to one common Active X container to exchange the contained data. In this situation it is not clear how to provide access for the both Slaves to the same container and were is better the container to store.

2. One Modbus Slave Simulator installed on one PC can simultaneously simulate two Slaves. The communication with the Slaves is provided via two separate serial ports. For example, one port uses RS232 connector, the other - USB connector and special adapter. However, I didn’t meet a Modbus Slave simulator which can simulate two or more Slaves.

I am sure that I am not the first who try to solve a similar problem, because the situations are very often happens when new systems are designed. Please, help me to solve the problem or share your opinion
how to find the solution.

Sorry, that I could not shorter explain the question.

Thank you in advance for your answer.
I have a generic inhouse Modslave.EXE application that responds to any Modbus Slave address it would see through a single serial port such as RS485 multidrop. email [email protected]

If you have a VB6 development system I can share the source so as to tie multiple slaves together as required.
My dll Shortbus allows the easy creation of a slave device using Visual Studio and .NET. You can control the interaction by instantiating two slave devices.