It depends on what kind of ACOPOS you have:
Standard ACOPOS has 5 inputs: 2X trigger inputs, Positive Limit, Negative Limit, and home. It also has an enable input for the STO function, but I'm not counting it.
The ACOPOSmulit has 2 inputs per slice, even if it's a dual axis: 2X trigger inputs
ACOPOSmicro has varying amounts of inputs depending on the flavor.
ACOPOS VFD drives are re-branded Schneider Altivar drives (312, 32, etc) and I never bothered to figure out the inputs because I've never used them.
The new ACOPOS P3, I assume, has 5 inputs like the standard it is replacing, but I've never used it, so I don't know.
On the Standard and Multi, any input can be reassigned to act like any other input (so the trigger inputs on multi can easily be used as limit switch or homing inputs). Also, the standard and multi have AC130 cards that can add more IO to the drive.
The trigger inputs have a resolution of 50 microseconds, not sure if limit and home inputs have the same speed on the standard. The new P3 drives are faster, don't know the numbers.
All technical information can be found in the easy to find PDFs on br-automation.com