On Jan 6, 17:58, Tom Leffingwell wrote: If you know its address, try to access the CSR from ODT. For example, if the CSR is at 772410 (which is the default) then if you type that address at the ODT prompt, followed by a '/' (without the quotes), you should see the contents of the CSR. If there's nothing at that address, trying to read it will cause a bus timeout, and all you'll get is a question mark and a new prompt. Probably the Microcomputer and Memories Handbook 1982 is your best bet, as it covers the 11/23, LSI-11 and 11/2, various memory boards (including your MSV11-D and MSV11-L), and has sections on the processors, architecture, and so on. You sometimes see them on EBay. I think that was the last (or 2nd-last) QBus CPU/memory handbook. There are at least one or two earlier editions that would have the same general infomation, but not the specific bits about 11/23 and contemporary memory, or 22-bit operation. There's a companion volume, PDP-11 Microcomputer Interfaces 1983-84, which you'd find useful. It has all the information about the BA11-M/N/S backplanes and many peripherals, including your DRV11-B. Apart from that, have you looked at the Micronotes at http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/hardwar… ? -- Pete Peter Turnbull Network Manager University of York