To piggy back Steve's excellent answer, most industrial label printers support this kind of interface as well. Here is a simple example I blogged about last year:
Industrial Label Printing with MII?
I have also come across a few legacy/custom shop floor systems that I have been able to integrate with this agent and therefore extend their useful life. 99% of the time though you will probably be dealing with a one way signal from a barcode scanner or weight scale.
Regards,
Christian
