> > Presumably you and the red tape producers have asked the questions:

> > - What do we want this to do or achieve that a properly designed
> > processor based solution cannot achieve?
> >
> > - Is the proposed solution really free of the issues which causes us
> > to reject a properly designed processor based solution?
> >
> > - Why do we believe that?
> >
> > - Do we genuinely believe that answer?
> >
> > - Iterate the prior two questions until the answer to the prior
> > question is "Of course not! Are you mad? This is just "political"
> > expediency!"

> > If you are handling crucial human safety and/or big dollars (eg
> > nuclear station shutdown sequences, launchpad umbilical detachment,
> > pyro sdafing, interlocks to life threatening system, Tokamac run up /
> > shut down cycling =A0etc) do people really think that the "programming"
> > which goes into a logic replacement system, and/or the risk of
> > marginal conditions (undetected race condition, lock into forbidden
> > state, go mad on glitch, ...) really make it inherently safer than a
> > properly designed, fail safe, redundant processor based system? Do you
> > believe their answwer? Iterate ... :-) .

> A lot of other people have commented further on this, but what it
> comes down to is this: Yes, one of the end users will be nuclear power
> stations. This product is nowhere near the "nuclear" part of the
> facility, but all the same red tape applies. We can produce a
> microprocessor version, there is a path to getting the software
> accepted, the process is so onerous that it makes the project an
> economical non-starter.

OK. That answers most of the above questions - it's not necessarily
better or safer etc but it's achievable this way.

FPGA despite their many merits are probably excluded if they load from
external memory as some people may think this makes them
indistinguishable from being programmable - regardless of the
arguments for or against, it's not an argument you want to have to get
into.

CPLD looks good - almost certainly able to meet your needs and is
essentially as  self contained as a block of discrete parts  logic.

Ladder logic may shorten the learning process and also allow
comfortable comparison with the old solution for lookers on. "This is
just like the relay solution because ..."

Martin's  suggested
http://digilentinc.com/Products/Detail.cfm?NavPath=3D2,400,798&Prod=3DCMOD
looks like a good place to start looking for rolling-your-own product
in small volume.





  Russell

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