27 Jul
2014
27 Jul
'14
12:32 p.m.
I don't know how ECO's (if any) were managed -
and not sure if the
equations on the schematic pages were kept up-to-date. I have a fuzzy
memory that the PLDs were socketed.
They wern't in my 11/730. I desolded and read out an example of every one
of them (what I mean by that is in some cases a PAL is repeated, not just
the type of blank chip but also the programming. In that case I only
desodlered oen fo them).
DEC didn't use IC sockets much. Maybe for reliability reasons, maybe
becasue there wasn't that much space ebtween adjacent boards in the
backplane [1]. I rememebr an Omnibus EPROM board where al lthe EPROMs
(1702As) were soldered in. Of course in-system programmign fo those is
impossible you have to put silly voltages on the data pins, etc. So what
DEC did was to run al the RPOM conenctions edge fingers on the top at one
side of the board, all the signals to link to them to fingers on the
other side fo the board. For normal operation you fitted jumper block
conenctors, for programmign I guess you linked a programemr to said top
conenctors. That's how much DEC avoided DIL sockets...
[1] Nothing to do with DEC, but when workign on my HP11305 disk cotnroller
I noticed that if you socketed 2 of the 5 microcode PROMs they would foul
the mains transformer. So my plan was to desolder the ROMS to dump them,
put sockets for the 3 I could, and alas, solder the last 2 back in place.
Only after removign them di I notice that the holes for those last 2 PROMS
(and AFAIK only those 2 ICs) were massive. Large enough to fit those
flsuh-with-the-board socket contacts. Which of course I ordered and
fitted. Yes, HP had actualy thoguth you might want to socket the microcode
ROMs..
-tony