On Thu, 3 Apr 2003, Ethan Dicks wrote:
> --- Tothwolf <tothwolf_at_concentric.net> wrote:
> > On Wed, 2 Apr 2003, Patrick Rigney wrote:
> >
> > > Does anyone recognize these three boards?
> > >
> > > http://www.rigneyfamily.com/patrick/
> >
> > ...which is similar to what you see in older SGI and VAX systems.
>
> That much is true. DEC (don't know about SGI) went to "PMI" - Private
> Memory Interconnect - to get around problems with address bus width and
> memory speeds with processors above the MicroVAX-I (the Qbus is limited
> to 22 address bits and about 3MB/sec transfer rate).
The older SGI systems that used a Multibus backplane had a similar PMI
like connection between the processor board and memory boards. Later
systems with a (custom) VME backplane also used interconnects, but they
were made with small pc boards and connectors instead of ribbon cable. If
memory serves, the memory boards didn't need those interconnect boards,
but many other board sets did, such as the video/display boards. I do have
several standard VME boards installed onto adapter frames that are plugged
into some of my (currently inaccessible) SGI systems.
> > (Can anyone verify if the 6821/6822 are some sort of bus interface
> > chips?)
>
> They are not. The 6821 is a common "Parallel Interface Adapter". It
> has two 8-bit parallel ports, several handshaking lines and a couple of
> internal timers. It is functionally equivalent to the MOS 6520, and is
> somewhat ancestral to chips like the 6522 and 6526. They are commonly
> used in 1970s and 1980s gear to strobe keyboard matrices, to drive
> external parallel devices, and to control LED and LCD displays (there's
> a 6520 on the display board on a Rockwell AIM-65, for example - I've put
> a 6821 in mine for testing).
I have to wonder then, if that connector might not be some kind of
bulkhead connector. Later SGI systems (1990-1994) use a 68 pin header for
the bulkhead, which contains a number of serial ports and also connects to
another board that has a 7 segment diagnostic display, etc.
-Toth
Received on Thu Apr 03 2003 - 23:47:00 BST