Oh, thanks! I wonder how I missed that, looking at the prints? (The drawings have these nice dark arrowheads to indicate backplane connections.) I just visually blew past it, I guess. BH1 is also used there (for SWMIB21 H); and on the previous page, the STOP L output is on AE1, and MTOE L (whatever that is) can be fed from AK1. Not quite sure how a Q22 memory card causes the problem, electrically, since those lines are inputs on the memory card, so it's an input<->input connection (i.e. voltage sources in TTL), but obviously it does. And I also don't see why Q18 cards are a problem; BDAL16 and 17 are AC1 and AD1 respectively, which I don't see in the 'extra pins' list for the LSI-11/2. Oh well, not too important to track it down. Thanks again for catching my miss! Wow, it's been a loooong time since I worked with an LSI-11 - about 40 years! :-) Noel