VAXen at home

Ethan Dicks ethan.dicks at gmail.com
Thu Oct 18 03:09:21 CDT 2007


On 10/18/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> The R80 has an 8085 in it, with rows of 8355/8755 (ROM/IO chips) IIRC.
> There's an interesting diagnostic facility on one of the boards
> consisting of a couple of hex switches, 8 LEDs and some momentary
> switches.

I remember fiddling with those once or twice, long ago.

> From what I recall, amongst other things you can read any
> location in the 8085's memory space...

Interesting.  Didn't know they were that flexible.

> If you have the tape drive versions, there's a normal RL-style connector
> on the CPU distribution panel, so presumanly you can cable up an external
> RL02.

ISTR that was the standard arrangement, just that the integral RL02
routed the cable such that it perfectly reached the I/O panel.  One
could still route the signal to an external drive if desired (which we
did once or twice for reasons I now cannot recall).

> Can you use an RL01, I wonder. No idea why you'd wnat to, but the manuals
> don't say one way or the other, so I am curious.

Good question.  Back in the day, I owned RL01 drives (since they were
under $200 and RL02s at the time were over $1000), but we never had
RL01s where we used VAXen.  ISTR there was something about being able
to use RL02s but not RL01s with the RL278 interface on a DECmate I,
but I also have not had the chance to explore that, either.

If you had one handy, it might make an interesting experiment.
There's no reason why it should break anything, but the
driver/controller might attempt to seek to a non-existent cylinder on
an RL01.

> I find it impressive that you can build _any_ VAX using standard chips
> (OK, with some PALs, and the memory ECC gate arrays from an 11/750 (I
> think), but the latter are hardly an important part of the CPU) on 3
> hex-height DEC boards.

I was pretty impressed when I saw the guts of an 11/750 for the first
time - it was so much smaller than an 11/780.  I, too, was impressed
when I saw all of that essential functionality in an 11/730.  My first
MicroVAX was even more amazing, but that's another product line and
another topic.

-ethan



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