Why no Universal I/O pins in PLCs?

Our company manufactures equipment for heating and cooling processes so we mostly use HVAC controllers.
It's been at least 7-8 years since these controllers make use of Universal I/O pins but I have never seen any major PLC brands make use of them.
For example one of the controller we use supports the following options for the configuration of single IO pin and is configurable through its programming environment.



Unfortunately it can't be configured as digital output.

some smaller equipment t with limited io has that such as Fisher Fb103's but larger scale I thing that would be a nightmare...

I think there are some issues using this method but not sure. Some of the relay replacement types have this type of variable input particularly the Mitsubishi one but that is just on inputs I believe. Quite a few have variable outputs includin PWM and the like. Good question!

National Instruments has a controller with universal I/O's. The downside is that its only TTL (5V). Its mostly desgined for laboratory and R&D use, not for industry.

The problem with the universal I/O is how to construct the transistors/opto couplers before the I/O so that it works both ways.

But then again, i wonder if the manufacturers would gain anything from having universal I/O. It would require more components, which is a source of trouble, as well as a higher price and more complicated design.

ojz0r said:

It would require more components, which is a source of trouble, as well as a higher price and more complicated design.

Click to expand...

I think this is the main reason. Plus, unless you have only a tiny, tiny amount of I/O, you're going to need a chunk of digital in, a chunk of digital out, a chunk of analog in, and maybe some analog out. It makes more sense to me to have them all grouped together in their own purpose built card.

My analogy: how many professional tradesman do you see rock up with an all-in-one leatherman tool and nothing else? Sure, they've probably got one at home for doing lots of odd jobs, but at work it'd be a pain. They'll have a complete set of screwdrivers, spanners, ratchets, knives, pliers, etc.

ASF, what a great analogy, you are on the right track to be a great helper.

its way to expensive to put all i/o in universal.
the reason the controllers ar doing this is to reduce the connections.