[Info-vax] VAX RDMs (Remote Diagnostic Modules)

[Johnny Billquist]

On 2011-11-16 18.41, Bill Pechter wrote:
> In article<1c7dp8-e55.ln1 at Ubuntu.mike-r.com>,
> Henry Crun<mike at rechtman.com>  wrote:
>> On 16/11/11 17:11, Bob Koehler wrote:
>>> In
>> article<272ef8f8-4d9b-4950-99e0-a50e0e7886b7 at b32g2000yqn.googlegroups.com>,
>> vaxorcist<vaxorcist at googlemail.com>   writes:
>>>>
>>>> Surely a modem, but what else? Another RDM or a special module or
>>>> computer for
>>>> remote diagnosis?
>>>
>>>      Could have varied, but an LA36 ahrd copy terminal would have been
>>>      sufficient.
>> Actually I seem to recall (could be wrong, though) that LA36's were current
>> loop, and could not talk to a standard modem. You would probably need an LA120,
>> or (slower) LA70(?)
>> I remember the RDM on a PDP 11/70 - DEC could only dial in if we switched from
>> local to remote console (IIRC a rotary switch on the front panel)
>>
>> --
>> Mike R.
>> Home: http://alpha.mike-r.com/
>> QOTD: http://alpha.mike-r.com/php/qotd.php
>> No Micro$oft products were used in the URLs above, or in preparing this message.
>> Recommended reading: http://www.catb.org/~esr/faqs/smart-questions.html#before
>>
>
> IIRC the RDC had a special protocol to interface with the RDM's.
> It was something like swapping bits in each byte transgered... bit6
> rings a bell in the back of my mind.
>
> That's why you couldn't just dial into any 11/70 with an RDC board.
> The board also let it bus snoop and send things like unibus states to
> the remote engineer.  Great for stuff like hangs and unibus timeouts.

I don't remember the details now, and I don't have any documentation 
nearby, but I don't think it had any special protocol.
If you hooked up the RDC front panel on the 11/70, you replaced the old 
front panel. The RDC front panel have a 8008, or somesuch, with a simple 
command line interface, where you can do all the same stuff as you could 
do from the old front panel with LEDs and switches. That obviously meant 
that you can examine all of memory, pretty much check the Unibus, as 
well as CPU states, and so on. But it does not allow you any more 
abilities than the normal front panel does. After all, it is just a plug 
in replacement, which uses the serial port and a microprocessor instead 
of the lamps and switches. They communicate over the same flat cables to 
the actual machine anyway.

And the command set for the RDC is somewhat simple, but it have the 
commands you'd expect, such as examine, deposit, step, run, halt, and so 
on. The normal console terminal also happens to run through this when 
the RDC is installed. As usual, ^P is what you used to get to the RDC 
instead of talking normal to the machine...

(All with reservation that I might have forgotten and mixed things up, 
but I do know where there is atleast the reference card for the RDC 
command set, even if I can't get hold of it right now...)

	Johnny