Micrologix 1000 STI questions

I'm running in the free emulator, no hardware available. I can't seem to figure out how to get the STI to fire. It seems this should be one of the easiest things to get working. I'm puzzled.

I have a simple rung in STI_INT of " INT ADD N7:20 1 N7:22". I'm just adding 1 with each call since I can't see a simple INC instruction anywhere. I see no changes in N7:22 and I have tried replacing the ADD with a simple bit toggle and can't see it changing. I'm thinking the STI_INT program file isn't getting called.

The timer is enabled with the interval set to 50. The docs say I don't have to use the STS instruction but I am puzzled about the file number to pass if I do call it, and what I should see in S:31 for the 1000 defaults. Is the STS file number 5 because that's the program file for the STI_INT in the 1000?

Welcome to the Forum!
See this link I found with Google. I have no idea if it will help.
http://www.judiwa.com/2011/02/02/how-to-setup-micrologix-sti-function/

Keep in mind there are some instructions available that the Emulate software won't run. Maybe just PID stuff. Off the top of my head, I can't remember what they are but someone on here knows and should jump in.

I'm running the RSLogix Micro Starter Lite. I've read the Micrologix 1000 STI section and the STI help in the IDE. The image from the google search is intriguing but I don't find a user interrupt enable in the micrologix 1000 data files. It's got to be some simple thing I'm missing. Since STI_INT is fixed at program file 5, it should just run if I meet all of the init requirements.