The ON+g+ENTER self test menu has 3 options the first of which turns on all the display segments. If you next press the roll-down key it will turn off half of them. Press it again to turn on the other half. The next press will turn them all back on again. This is all documented.
What's undocumented is what happens if you press and hold the roll-down key. On the 12C+ the display will rapidly cycle through the 3 displays a couple of times then terminate the self test showing the X register. On the 15C LE it will do the same then show the current program line. When you release the roll-down key it will run the program starting at that point.
This is pretty weird and a little scary, what's the self test doing running a program? I haven't seen anything like the other self tests that corrupt program memory but I haven't done much testing of this yet.
-Katie
Edited: 19 Sept 2011, 11:52 p.m.