What leeveney mentions, one of our many built-in I/O features, is one of several "best kept secrets" of our I/O, so I'm glad you brought it up!
For sure you'll want to check out the commands in the Digital Point section of the command reference, like the Get On-Latch leeveney alludes to. Ben would probably go a step further and suggest you print this quick-reference (it once fit on a page--we've added a lot more commands since those days!) to study and memorize/wallpaper favorite room. But that might be a bit extreme.
If you inspect your Ethernet I/O (PAC or older brains too) directly via PAC Manager, you'll see these digital points features right there at the rack. The PAC Control commands simply read these values on the brain.
This distribution of intelligence frees up your controller from having to keep track of these things constantly (or worry about missing something in your network goes down, etc.). And the "brain" on the rack won't miss anything (like a quick on/off) that your controller logic might.
Also built-in on the analog side: min/max values w/no programming needed.
Happy latch reading!