On Dec 31 2005, 19:32, Charles wrote: 10% is not minimal. It might be enough to make a difference. The switches are just mapped to a register that the boot ROMs -- or indeed any other code -- can read. It's the Configuration and Display Register (CDR) at 777524. It's nothing to do with microcode, nor is it anything that directly affects the hardware. The effect of the switches depends entirely on how they're interpreted by the bootstrap code, and the description you list above is correct for the original BDV11 bootstrap and for the early PDP-11/23plus bootstrap (which was almost the same). It's not correct for the microPDP-11/23 bootstraps. The early microPDP-11/23 (KDF11-BE) bootstrap used switch 1-8 ON to set up for ANSI VDU console terminal, and 1-7 ON to enable the quick memory diagnostic. Usually 1-1 to 1-4 would also be on and 1-5 and 1-6 off, to select the MSCP aiutoboot. All off would inhibit autoboot. All six on would loop the self-test. There were 25 defined boot settings, and 37 reserved or unused. If you tell us what ROMs you have on the board we can tell what firmware version you have. Looks like bootstrap setup code. The first few words are Looks like an 11/23plus bootstrap, rather than, say, a microPDP-11/23 boot. No copying involved. When you're using ODT, you use 18-bit addressing (at least on this CPU), and 173000 then is simply the 8th bank of memory (bank 7, counting from zero). 773000 is the I/O page, where the bootstrap lives, and apparewntly you realised both those facts, but perhaps didn't realise that when the CPU is running, any reference to bank 7 (160000-177777) asserts the BBS7 (Bus Bank Select 7) signal so when a program accesses 173000, it actually gets the boot ROM. That's hardwired, in fact; it doesn't even use the MMU. In effect, accessing the highest-addressable bank always gets the I/O page (this is a slight oversimplification, because it depends on devices recognising the BBS7 signal, but it will do for this discussion). False trail. Start by double-checking all the jumpers, especially J16/17/18/19 (you probably want J18-19 and nothing on 16 or 17). Check even the things that should never have changed, eg that the test jumpers are all in the correct places (J6-7, J8-9, J20-21, J34-35 not 33, J26-27 not 25). Check there's nothing on J15, that J22/23/24 are set for whatever type of ROM/EPROM you have, etc. -- Pete Peter Turnbull Network Manager University of York