PDP-8 VT8-E - test-drb@ccmp.vtda.org

21 Jul 2014

At 12:00 AM 7/21/2014, Eric Smith wrote:
...
 On Sun, Jul 20, 2014 at 8:10 PM, Rick Murphy <rick
at rickmurphy.net> wrote:
  I don't know anyting about a PDP-14, 
The machine is question is a VT14, not a PDP-14.  The VT14 is a
specialized terminal used to develop ladder logic programs for a
PDP-14.
  but it it used a VT8-E, 
It didn't. 
Full circle. There seem to be two sets of assertions here.
One that a VT14 used the VT8-E board set, and another that it used a
different set for video.
You're asserting that it's not a VT8-E, which means that many of my
assumptions were wrong. In one of it's modes, which would allow it to
be a good display device, the VT8-E uses DMA from main memory to drive
a bitmap display. That memory has to be on the Omnibus, and has to be
read/write to be of any value. That causes the following assumption:
...
   it had to be
an Omnibus machine with Omnibus memory, 
It was.
  so it could easily be turned into a PDP-8/E

That doesn't necessarily follow, any more than it would follow that
because some sort of embedded device contains a Z80 CPU chip, it can
easily be turned into a CP/M system. 
You have a KK8-E cpu and the standard Omnibus which can accept a range
of peripherals. You can't usually plug extra hardware into an embedded
system.
...
   with the right
CPU card set. 
It had a KK8-E CPU card set.  To get it to run general-purpose PDP-8
software, you're going to have to replace the memory, as the MR8-F
isn't too useful for that. 
I see. Perhaps it's the case that the VT14 doesn't have Omnibus RAM,
and only has a MR8-F which the KK8-E CPU uses to run the code that
manages the display. This is the first I've heard of the MR8-F, which
apparently has onboard RAM to provide the read/write memory needed.
(The older Ombibus ROM devices shadowed core.)
...
 The power supply isn't suitable for core
memory, but it might be for semiconductor.  The keyboard and display
are going to be useless.  The backplane, CPU, power supply, and
teletype interface are the only parts of the VT14 that you're going to
end up using.  I wouldn't call that "easy", nor would I call the
result a "PDP-8/E". 
Yes, and the power supply isn't useful unless you're using something
other than core. And how many slots does the backplane have?  Yes, it's
possible, but given what I know now it's not easy. It's a source for a
donor CPU board set, and maybe a TTY interface (assuming it's KL8
compatible) and that's about it. Possibly workable with the recent
semiconductor memory boards. Oh, and of course, no front panel, making
it hard to do anything useful unless you reprogram the MR8-F.
         -Rick