Probs w. M3119 CXY08 MUX on VAX VMS 7.3
elson at pico-systems.com
Tue Aug 18 21:27:27 CDT 2015
On 08/18/2015 01:00 PM, Johnny Billquist wrote:
> The floating address space was pretty much there from the
> start for the Unibus, even before you had "large" systems.
> For most controllers, only the first one has a fixed
> address, and all others were assigned from the floating
> space. Makes sense, as it was just too costly to
> statically assign space in the I/O page for all possibly
> configurations you could imagine.
The CAPABILITY to do it was always there, that is quite
true. But, most of the OLD PDP-11 devices had a VERY
limited selection of addresses. Now, some DID have
something like 6 address bits settable in a jumper or
wire-wrap field, but I know a number of devices had just a
couple DIP switches that limited you to 4 or 8 possible
addresses. I know on some old stuff I actually cut traces
and re-patched the address select bits to make them run at
My PDP-11 experience started in 1975, and was with stuff
that was probably almost a decade old even then.
>> In some cases, you had to force a device to be at a
>> address, possibly because a 3rd party device could not be
>> configured at
>> the address the DEC enumeration scheme wanted to put it
>> at. This was
>> pretty easy to do in later VMS systems.
> Very easy to do in RSX-11M-PLUS as well. A simple one line
> command, which can be done on the running system.
OK, I ran RSX-11M, but never M-PLUS. I remember doing
sysgens late at night to reconfigure the I/O addresses.
>> Unfortunately, this type of misconfiguration is fairly
>> hard to detect
>> with software. Later devices (MSCP) had an
>> autoconfiguration scheme
>> where the OS would assign the CSR and vector at boot time.
> Well, half correct anyway.
> The CSR is never autoassigned. It always is configured by
> switches or jumpers on the board. Some of the more modern
> controllers, like MSCP controllers, setup the vector
> through software.
OK, what I USED to know is just fading away! Yes, what you
say makes perfect sense.
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