You have a Pioneer. That was a lower model on which full-time was an option, but not often found. I doubt you have it.
The Cherokee has always offered two "flavors" of 4WD -- "Command-Trac" was a part-time only system (not to be used on hard surfaces or pavement), and "Selec-Trac" which in most years added an additional 4WD position for use on pavement, which is why it is called "full-time" -- you can just put it in that position and leave it there all the time, regardless of what kind of surface you drive on.
Lower your driver's side sun visor and you should have a sticker that tells you if you have Command-Trac or Selec-Trac.