If you decide you need interrupts, the DLV11 (MP-00055) has a simpile interrupt circuit built out of flops and gates. Neither, but your first one is close! :-) Actually, that design started as a CAD file (for KiCAD) that I got from Dave B; I munged on it until it was what I wanted. Those two signals were connected to that transceiver in Dave's original circuit; my design doesn't (as you discovered) actually use BPOK or BINIT, so they just stayed connected up, but unused. As Glen indicated, it actually takes 2 50-pin connectors. I don't think they'd have carried power through that connector. The spare lines might well be connected through. I haven't checked the pinout of the 50-pin Berg headers (which were the original, the 'D' connectors came later), but if they followed UNIBUS precedent, every other wire in the flat cable will be a ground, to help minimize cross-talk between lines with signals on them. Well, the QBUS wasn't designed to go through a cable, originally it was backplane only; so it doesn't have differential pairs, or anything like that. Noel