Spent the last couple of days tracking down a bug in the emulator; today I even had a couple of flight software guys helping me out. Their insight was invaluable. Without knowing how the low-level I/O routines work, I never would have figured it out. The problem turns out to be with the same addressing mode as the first I fixed. One of the AP101/S addressing modes with indexed, indirect, and its own flowchart to show how it works. This mode is so complicated that I might never get it completely right; maybe when we get the microcode listings I'll be able to do better.