Remember how in IM 2, the high byte comes from the I register and the low byte of the address for your ISR is random? That may have been true for the TI-83+, but I don't think it's true for the TI-83+SE and TI-84+(SE). A while ago, I did some tests on my TI-84+SE that suggested that in IM 2, the only vector that ever gets used is the FF one. Now, once again, I have written a slightly more advanced tester, based on MicrOS, to keep track of what vectors are issued. Attached is a program for this and its source. Be aware, this program erases all of your RAM. Run the program, and you just get a basic hex editor, starting at address 6200. Address 6200 is the start of a table keeping track of how often a particular IM 2 vector is used. Each entry is two-bytes, so to check how often 20h was used, go to 6240h. The only vector I have ever seen is FF (63FE). Does anybody else with TI-83+SE or TI-84+(SE) ever see a non-zero value in the 6200h to 63FDh range?

Yeah, DrDnar, I made a test like this a long time ago, and I can say that mine is random. It favors some addresses, but in the end, it's unpredictable.

I just ran mine and I get hits in random blobs about every 30 bytes.

Hmm... Sound interesting.  It would be nice if we didn't have to fill that huge space with all the same number.