Modbus protocol implementation

[golubovski]

Hello colleagues,

I need to use a PC with a LabVIEW application to serve as modbus master to talk to a single modbus slave that concentrates data from another modbus, where it is the master talking to around 30 instruments (slaves). I have no experience with implementing modbus protocol, and have downloaded the NI Modbus Toolkit. Does someone have experience with using this toolkit - there is no help/manual, and I'd appreciate an example diagram(s) showing me the typical implementation of the protocol (initiating modbus session, sending commands, reading data, ...).

Thanks in advance,

[tst]

The LLB does include a couple of examples.

[unclebump]

Are you talking modbus over the serial port or the ethernet port?? There are examples of both in the forums already.

[JB]

I have just finished an application that exchanges data through an ethernet modbus communication (PC=master and 1 slave). Please post again if you need further help.

[golubovski]

Thank you guys. It is a serial communication. Do I send/receive to the COM port just like for an ordinary RS232, or do the VIs take care of the VISA session and I just write/read bytes? Can you explain the logical (command) protocol in short - cmd, operand(s)...? I have no idea for the concept itself.

Thanks in advance,

[unclebump]

See this thread for the protocol manual.

http://forums.ni.com/ni/board/message?board.id=170&message.id=197677&query.id=96682#M197677

Attached is a serial query.

[golubovski]

Unclebump @all,

Thank you for the prompt support. In a week or so I will have some slaves to play with, and will use this thread if needed again.

[lslnim]

I cannot find the address where to download NI ModbusToolkit.

Could you tell me?          Thanks!

[unclebump]

Here is the 8.2 version,

http://sine.ni.com/devzone/cda/epd/p/id/4756

[lslnim]

Thank you very much, unclebump!

I have downloaded it.