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

[Bill Pechter]

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/
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>

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.

Bill

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