Hi all,

I need to send data to a PLC which support modbus protocol only. I am new to this PLC field and the modbus protocol.

The data i need o send is an integer value. ie, The value read from a register of a controller. When i go through the internet and all, i found that there is RTU and ASCII framing.

If the data i need to send is for (eg 10), What will be the exact data format(data frame) in the modbus case

Can any one help me how can I do the above.

 

It really depends on what protocol the Modbus device you are talking to speaks. If it is very old, it could do Modbus ASCII channels are though that it is a standard Modbus RTU serial. You can get the protocol information from Modbus.org or you can get Modbus server from one of several communications companies.

Fred Loveless
Applications Manager
Kepware Technologies

 

The format of the modbus message is explained very well for those new to modbus at www.simplymodbus.ca/FAQ.htm

 

Are you developing the software to communicate with the PLC? if so, maybe you can find more details in www.modbus.org

Good Luck!

Gonzalo Jimenez Yamasaki
http://www.linkedin.com/in/gonzalojimenezyamasaki
http://sites.google.com/site/gonzalojimenezyamasaki/

 

You can do that with the OPC server for Modbus. It supports all data types. It comes also with a OPC client that you can use to enter your values. here is a link to it:

http://www.matrikonopc.com/opc-drivers/128/base-driver-details.aspx

Wassi Daoud
Global Solutions Architect
www.MatrikonOPC.com

 

Hi,

Modbus provides a rich set of functions by which it is possible to read values from PLC (Modbus Slave).

I think, you are going to develop Modbus Master. Please check the mode(ASCII or RTU) used by the PLC to send data. Your Master application should use the same mode used by the Slave PLC.

Please go though www.modbus.org site. There, you can download the standard specification which describes about Modbus working, its functions, framing. Also, you can download a lots of pdf files which describes about Modbus very well.

I will be very much happy, if my explanation could help you...