Aduke.1785
net.general
utcsrgv!utzoo!decvax!duke!dbl
Wed Feb 17 11:39:40 1982
Re: utcsrgv.125 :Info on PDP12
The PDP-12! Ahh, what fond memories I have...
As far as maintainability is concerned, most of what makes up the PDP-12
consists of logic modules out of DEC's old Flip Chip(TM) logic series.
Though this also means it has a tendency to give off a lot of heat.
Problems can be traced to the board and chip level, if you're up to it,
have a complete set of prints, and the diagnostics.  The 12, in case you
don't know, is a dual processor machine. The two processors, a more modern
version of the old LINC lab computer and an early version of the PDP-8,
share common memory, but do not operate concurrently. The LINC processor
has the instructions for accessing the D/A, A/D, relays, display scope,
and the LINCtapes (a little different than DECtapes, but not much). The
PDP-8 portion has most of the familiar PDP-8 instructions set, so most
PDP-8 software will run in 8-mode, and all terminal traffic is handled
through the PDP-8 I/O bus.
Programming can be a little hairy, for various reasons. You DO have to
do everything yourself, I/O routines, interrupt service, etc. but what
do you expect? Also the interrupt vector address and memory addressing
is handled differently by the two processors even though it is the same
memory. It has a reasonable editor which uses the display screen. Assembly
can take what seems like forever on the LINCtapes, but the assembler is
pretty nice, having things that you wouldn't expect to find such as a
conditional assembly facility.

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