On Fri, Feb 26, 2016 at 3:15 PM, Noel Chiappa <[email protected]> wrote:
> So I have some MM11-U UNIBUS core memory cards, and in trying to locate a > backplane to plug them into, I remembered a story I'd read on Guy's > Web-site > about some issues he'd had with parity and non-parity operation: > > http://www.shiresoft.com/pdp-11/11-10/index.html > > and mention of the backplanes as being specific to parity and non-parity > operation. So, I figured I'd better make sure what kind of MM11-U's I had, > and get the correct backplane (MF11-U or MF11-UP). So I looked at the > prints > sets, and... the part number for the parity and non-parity backplanes is > the > same. WTF? > > Extensive further digging finally turned up this, in the "MF11-U/UP core > memory system maintainence manual" (DEC-11-HMFMA-B-D, 3rd Printing, > November > 1974): > > 5.2.3 "Installation Procedure" > > "A backplane jumper is required from B1U1 to B2U1 for non-parity > memory. > This jumper should not be present for parity memory." > > Which makes sense. Apparently, for parity operation, SSYN is routed through > the M7259 Parity Controller, and it only issues the SSYN once it has > checked > that the parity is OK. So, on non-parity installations, the 'proto-SSYN' > from > the rest of the memory is just hard-wired straight to the output to the > UNIBUS (hence the jumper). > > > Also, since the MM11-L system uses the same parity controller board > (M7259), > it seems a reasonable conclusion that there should be a similar jumper on > the > MF11-L backplane, and I have found such a jumper on some MF11-L backplanes, > but I have yet to find anything in any DEC documentation about it. > > Speaking of MM11-L/ME11-L/MF11-L backplanes, there appear to be at least > four > different etch revisions (and I suspect the earliest one cannot be tweaked > to > run parity, since it _doesn't_ have that jumper on it). But that's for > another > day! > > Noel > Very useful, thanks. I will try this. Bill -- @ BillDeg: Web: vintagecomputer.net Twitter: @billdeg <https://twitter.com/billdeg> Youtube: @billdeg <https://www.youtube.com/user/billdeg> Unauthorized Bio <http://www.vintagecomputer.net/readme.cfm>
