serial interface program using ladder logic

Hi,
I have to send some command to a device from PLC using RS485(serial comm).
Can you pls let me know how to write ladder logic for this.

Thanks in advance.

What is the hardware that you are using?

Regards,
Garry
http://www.accautomation.ca

The communication is btw AB 1766L32BXB PLC and VLT C51 AC drive.

Have you tried the manual for the drive? Chapter 5, modbus via rs-485 is native to the drive.

Yeah I saw that, the drive supports 485 cumminication.But i didnt have any idea how to communicate to the device.Pls give me some hint on how to code in ladder logic.

The fact that the drive supports Modbus should actually tell you something...
You need to talk modbus to the drive to be able to communicate with it.

I don't know if your model supports ModbusRTU, but a quick search for ML1400 and ModbusRTU leads to a AB document that states that this is indeed possible. But I guess you will have to set up Channel 0 to be ModbusRTU, to enable it.
What kind of function blocks you need I do not know, but it is likely not that difficult..

The Danfoss MudbusRTU manual should give you the hints you need to set up the telegrams needed:

http://www.danfoss.com/NR/rdonlyres/844E0F42-AB58-4EAD-A11B-BDAED985391D/0/ModbusRTUOperatingmanual20111117.pdf