how to code out for MODBUS RTU based application using VB C# ... i have a past work experience in RS232 using PIC16F MCU... but now i want to integrate a industrial controller having MODBUS RS485..

Hi, Jagath! If there are only a few situations you need to handle with Modbus RTU, I would suggest that you buy a “Modbus ActiveX” or “Modbus DLL”. Thus, you do not have to deal with timing between polls and read, especially there are many slaves involved, which could be painstaking and time taking.

the first step to define a hardware or technology how siemens or Allen Bradley or Schneider.

If you define that technology to use, then email me.

King Regards

leon>> the controller is open MODBUS RTU interface ...and i have separate programming tool for the controller ... other then HMI.

Usually you need to define some parameters,
1. Parity
2. Modbus Address
3. Speed (Baud rate)
4. Modbus code
5, Register

The three first parameters are common for all communication, so Modbus has some standar codes for read and write, but each device has a register modbus, this are like address for example the register 1000 - 1200 is inputs, if you need read the inputs then you need specify to code for read and the register number.

If you need info more specify should to read manual of device.

thks leon >>> as my controller just output the I/O values in an timely manner or cycle, and its a MODBUS RTU device.. my HMI application don't need any process control more over is a DAS. the issue in my code out is with the tagging, because all the values are just rushing out in a single text box, so just trying out with filters..