On Feb 6, 18:18, Allison J Parent wrote: RQDX1/2, Supports all the QBus controllers. OK, that's not very full :-) ignored Maybe it depends on the firmware then, but I can assure you that the bug certainly exists, and lots of people other than me found it and suffered return some flags in the top 4 bits of the SA register during initialisation. On the RQDX1 and RQDX2, the rest of the register contains zeros, and the driver code depends on that -- IIRC, there are three places where it does a BNE on the result. The RQDX3 of the same vintage as 5.01, however, returns the interrupt vector in the bottom bits of SA, so the BNE doesn't work as desired. Actually, there's slightly more to it than that, but that's the basics. -- Pete Peter Turnbull Dept. of Computer Science University of York