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

[Johnny Billquist]

On 2011-11-15 23.04, Rich Alderson wrote:
> Paul<useddec at gmail.com>  writes:
>
>> On Nov 15, 1:32=A0am, vaxorcist<vaxorc... at googlemail.com>  wrote:
>>> A question for former DEC technicians, System Managers&  whoever
>>> worked with RDMs:
>
>>> Several of the bigger VAXen had an RDM (Remote Diagnostic Module) as
>>> an option. In case of problems these RDM were connected via serial
>>> line and modem to one of the DDCs (DEC Diagnostic Centers).
>
>>> What kind of hardware was used on the other side (at the DEC
>>> Diagnostic Centers)?
>
>>> Surely a modem, but what else? Another RDM or a special module or
>>> computer for remote diagnosis?
>
>>> My VAX-11/750 has got an RDM and I would like to use it one day.
>
>> The 11/70 had a RDC as an option. I think I still have one around
>> here. I think tdey dialed into Colorado Springs.
>
> I was a systems programmer on two DEC-20s at a site that paid for that
> service (called KLINIK on the 36-bit product line).  The system to be
> looked at did not dial out to Colorado Springs; rather, a systems programmer
> would enable the KLINIK line, and place a call to DDC to let them know that
> it was possible to dial into the console.  After they had their way with
> the system, the line would be disabled until needed again.
>
> I don't imagine that the procedure was different for 16- or 32-bit systems...

Yeah, that sounds pretty much how I understood things worked. On the VAX 
86x0 machines, this is a key you turn to "remote enable", to enable the 
second console terminal port, and allow it to access the FE, so that all 
kind of dangerous stuff can be done on the machine. Normally you'd have 
it at "disable", so that the remote port either was totally deactivated, 
or else just worked as a normal serial port without access to the FE. 
The key have five positions: OFF, LOCAL DISABLE, LOCAL ENABLE, REMOTE 
DISABLE, REMOTE ENABLE

The 11/70 RDC front panel gives you something similar, except I don't 
think it ever becomes a separate serial line into the PDP-11 as such, 
but can only play on the "FE".

For the KL, wasn't there just a switch on the front for remote enable, 
or something like that (I'm trying to remember what switches you had, 
there wasn't that many...)

Anyway, you normally then have a modem on the remote diagnostics port. 
There is no normal, sensible way, for you to dial out using that modem, 
since it is sitting on a machine that might be pretty non-functional 
(that's when you wanted the remote diagnostics to look at it), so they 
would have to dial in to your place. And you had to enable the port, so 
that in normal operation, they could not dial in and fool around with 
the system (either by mistake, or malice).

The remote diagnostics center most likely had some software that could 
play with your system to do some basic troubleshooting, data collection 
and testing, but I bet in some cases, it ended up with a human at the 
other end working at the console trying to figure out what the problem 
could be.

And for all systems that I'm aware of, the RDM port is just a serial 
port, with an interface that looks pretty much like the console port 
boot monitor. So, you can hook up a normal terminal, and use that port 
just as you can the console port.

For the VAX 86x0 machines, I know that the console port command set is 
documented, including the features that could be used for remote 
diagnostics.
I seem to remember having some documentation for the RDC of the 11/70 as 
well.

	Johnny