Programmable logic controllers

Hi
Iam writing a report on I/O field devices and communication links field communications and need some help.
Also types of networking communication links used in PLCs & one protocol used in signal communications. if anyone has this imformation or any good web sites please pass this imformation to me
many thanks
simon

Here are a few that may help.
http://ourworld.cs.com/rahulsebos/
http://www.odva.org/
http://www.modbus.org/
You could also try http://www.ab.com
http://oeiweb.omron.com/ for a couple of PLC specific proprietary networks (DH+, Controller Link etc).
Hope this helps.

The Ultimate Fieldbus/industrial bus list

http://ourworld.cs.com/rahulsebos/Links.htm

It's a challenge to even scroll through it. Make sure you scroll beyond Fieldbus, because then it goes alphabetical for miles

Dan