I am doing a project on controlling the plc by using raspberry pi. Any one please suggest some sample coding and tutorial regarding this project. am already finished a coding part to connect a control model to control plc. Now I am struck with how to interface and gathering information from plc to pi.
There are many different ways to interface with a PLC. Depending on what protocols they communicate with.
Here's some links on two of those protocols
Step7 for Siemens PLCS S7-200,S7-1200 and S7-1500: http://simplyautomationized.blogspot.com/2014/12/raspberry-pi-getting-data-from-s7-1200.html
Modbus TCP for many others: using pymodbus this blogger was turning on a PLC from his pi built lightswitch: http://simplyautomationized.blogspot.com/2013/09/home-automation-project-part-3-webapp.html
Hope that helps.
Been able to control a Koyo DL-06 with ethernet as well: http://simplyautomationized.blogspot.com/2015/04/raspberry-pi-getting-data-from-koyo-dl.html
You can use new PLC platform Speedplc for Raspberry Pi.