One of possible applications for iMX233-OLinuXino we had in mind when designed it was to create platform which to be used as low cost Linux PLC.
Now this is about to become reality with Jeroends project http://leachy.homeip.net/olinuxino/
For now the project code talks to MODBUS devices and I2C devices (including MOD-IO stackable IO module) and OLinuXino GPIOs as well.
As MODBUS is de-facto standard for industrial distributed I/O you can use this demo to read PLC or HMI interfaces if they support MODBUD through TCP/IP.
There is step by step tutorial for what you have to do to install the necessary tools and run your first PLC project with OLinuXino.
Well done Jeroends !