hickman...
Don't limit yourself by thinking that a "Stamp" has "so few I/O".
I/O can serve as an "address/data bus". As fast as those guys go, you can "communicate" with a multitude of other "Stamp" devices in very reasonable time. There might be noise issues but they can be overcome. You would have to develop a "Bus Controller" to manage traffic.
You could have one Stamp act as the Boss (Master Control) and several others as Slaves (Local Control).
All of those Stamps could be on the same card. You could end up with a True Multi-Processor in the sense that you can have ten people doing whatever it is that they do at the same time... think Military Maneuvers... think Generals and Platoon Sergeants.
The Sergents get their "orders" and use their "resources" to do what has to be done. Meanwhile, they keep the General up-to-date on the field situation - as required. The General then makes tactical changes in his orders as required to meet the changing field conditions.
And... the great part is... if you use Stamps that speak "C", then you can literally use "English Phrases" for evaluations and subsequent commands! In "C" you can name your own functions - as in...
"If Station-1_has_Finished_Processing_the_Part" then "Send_the_Part_to_Station-2".
It really ain't that hard to do. And if you do, then you are doing better than most PLC designers!
It should be readily apparent that PLC designers are trying to develop "quasi-multi-processing" (heavy on the "quasi") with software while still using the basic 8088 design. That is, they are using a "Grafcet" type scheme to make you feel that you are getting 2, 3, or more for the price of one!
Peter and his "Delta Computers" are a great example of what I'm talking about. On Peter's motion cards, all he wants is some direction... a command... "Tell me what you want and I'll take it from there!"
A Delta Computer Motion Card is what it says it is... a stand-alone Computer (it's faster than most, if not all, PLC Processors). It gets it's commands through a sorta-kinda data bus... that is, it gets its' marching orders through a set of dedicated V-Mem locations in the PLC. Those V-Mem locations (PLC-to-Delta) are updated on "PLC-time".
So anyway, hickman... if you play this game, you'll be playing up there with the BIG-BOY(S)... Peter and his Delta Computer among others.
As a mental challenge (BTW, speaking of "mental challenges", I will be posting some general, only general, thoughts on the PLC VENDOR SECURITY CODE), this is a GREAT exercise! And can easily grow to be more than simply a challenge - it could be a career!
Don't let anyone discourage you with phrases such as... "Don't Re-Invent the Wheel", or, "If it ain't Broke, Don't Fix It". A lot mo'better has been accomplished by "Re-Inventing the _______" and "Fixing the damned _______ that ain't broken!". Sometimes it's a case of, "If it ain't broken... Break the GD Thing!"
Be "System-Minded" - that means, plant-wide! Look at "bottom-line", i.e. profit!
If der ain't no profit... der ain't no jobs!
Imagination is what makes the World-go-'Round!"