At 10:32 AM 7/10/97 -0400, you wrote:

>>When we took a photo of the cabinet (with a flash) it went haywire and
>>relays clicked all over the place - fortunately the hardware safety
>>interlocks prevented the generators starting...
>>
>>The point is that opaque masking tape was not opaque the the UV from an
>>electronic flash. We had to put aluminium foil (doubled over to avoid
>>pin holes) then cover this with tape to be sure we didn't let any other
>>light in...

>Did you track your flash-bulb problem down to a specific uninitialized
>register?  I can't find mine, and I hate solving a problem without knowing
>what the answer was.  It unnerves me.

Both controllers were set up as state machines, so there were negligble
opportunities for uninitialised variables. It seems the direction registers
were momentarily inverted when the UV burst from the flash hit. One thing
we did as a precaution was to refresh the direction registers upon each
state change detected. WHen didn't have time to investigate any further and
found no other software precautions/changes necessary.

As a matter of policy ALL our windowed chips are covered with full opaque
metal tabs to be as sure as possible there is no chance of any light
causing alteration of operation.

It stands to reason that chips will have some susceptibility, especially
with design tolerances getting ever smaller and the energy per gate being
very small indeed.

Prior to the UV flash we noticed no difference in operation from normal
incandescent light bulbs, though these were MC68705R5S dies which were
NMOS and were made around 1988 so die sizes were a bit larger than etc...

Maybe some subtle thing like a flag or set of memory locations are being
changed - it would be quite easy to set up a test - that is a full
RAM XOR to report which RAM locations and/or flags change.

This would be a simple, yet most interesting experiment.

I know of one chap around 1985 that used a 2708 fully programmed and watched
how the bits were slowly erased by exposure to daylight as a possible
means to determine UV strength - I think consistency was a problem...

Rgds

Mike
Perth, Western Australia


Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.
                                                                       Massen