yet another pdp-11 in fgpa

allison ajp166 at
Wed Jun 30 20:43:51 CDT 2010

On 06/30/2010 09:17 PM, Eric Smith wrote:
> allison wrote:
>> It was my understanding that the 11/70 continued as a grandfathered
>> EMI and the new multiple cpu died due to EMI issues (plethora of cables
>> and multiple racks) and [...]
> That sounds *much* more plausible than the problem being that the flat 
> cables were a maintenance/serviceability issue, as has often been 
> reported.

They were but, changing it meant making the grandfathering a problem.  
There were far to many cables that
could easily be swapped and cause a failure or more commonly a no run 
case till it was sorted out.
Around that time a New engineering group CSSE wich was part of Central 
engineering but funded by
filed service was in existence to solve manufacturing quality and field 
maintainability issues. That was
spawned by FA&T (factory assemble and test) because supposedly 
interchangeable parts weren't
so and systems would not work in the field (early 70s).  So the cable 
issue was very real but it was
not the sole reason.

> Of course, with enough effort, they could have solved the problem, but 
> likely didn't want to for theother reasons you mentioned.

Therein lies the problem, FCC rules of the time meant if you redesign it 
your committed
to "fix" the RFI issue.  That meant only ECOs and retrofitable options.  
The VAX and later
PDP-11 machines shows that packaging impact.

Also for those that were in DEC there was always a bit of a split in 
product groups where some
wanted to  keep tweaking the design for cost and speed and those that 
wanted a whole new
challenge and direction.  Some of that shows in the various ways the 
PDP-8 and PDP11 were
implemented over the years.

Just trying to keep up with that was a experience.  My years in DEC 
engineering were among the
best in my career.


> Eric

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