Re: Reading serial port lines

From: David Reeve (dree4456_at_big-pond.net.au)
Date: 10/14/04 

Date: Thu, 14 Oct 2004 08:51:52 GMT

"L D Blake" <not@any.adr> wrote in message
news:jfkrm0hhfbo2bnnmp3fjeq0s35nsd2oui8@4ax.com...
> On Thu, 14 Oct 2004 00:49:31 GMT, "David Reeve" <dree4456@big-pond.net.au>
> wrote:
>
> >Errr....logic thresholds have everything to do with it, this is a real
world
> >logic device we are talking about. Start to think about a formal
engineering
> >description of the situation and you'll see what I mean.
>
> David,
> In a peripheral way logic levels do matter... but I seriously doubt it's
much
> of an issue when you have a capacitor being discharged every time the
switch
> bounces closed and charging only a few millivolts while it's bounced open.
>
> Remember, we are talking about an event that might last less than a
hundredth
> of a second... with perhaps a dozen or so sub-events lasting only a couple
of
> milliseconds each. It's not like we are putting a logic gate into long
term
> abiguity and, given that most IO driver chips now use schmidt inputs they
are
> hysterisis guarded to begin with.
>
> I've done this hundreds of times on some pretty groddy switches and it's
never
> been a problem yet.
>

I think we are comparing 'what you can get away with' versus good
engineering practice. To get back to programming, an analogous situation is
to be found in how well one engineers the interaction between the components
of a multithreaded environment. We could both agree that a race hazard
exists, but differ markedly in terms of whether it is likely to come and
bite us. When designing electronics for a production environment, or
designing software for commercial release, I refuse to be impressed by the
argument 'well it works doesn't it' . To my mind it must be demonstrably
correct by design and calculation, including multiple belts and braces where
adequate theory can't be found.

Dave

Relevant Pages

  • Re: Rant: Software jobs, WTF?
    ... 99.9999% of Software "Engineering" isn't engineering. ... AN ACT providing for the licensure of software designers' ... practice software designing. ... or fail to renew the license of a software designer ...
    (rec.sport.football.college)
  • Re: Your input is needed for the design of a new type of coffee machine
    ... of coffee machine with a group of my fellow students. ... My initial response is that this is a good project, for Industrial Design students, not engineering students. ... It is all about designing a product for people, ...
    (alt.coffee)
  • Re: Griffin Calls STS, ISS "Mistakes"
    ... > Arianespace was under the impression that designing the Ariane ... > launchers to be expendable would mean that the engineering margins ... ammount of engineering work but you do not have to use lesser margins, ...
    (sci.space.policy)
  • Re: Bent RC Frame
    ... I believe the engineering was designed to take upward shock ... trash the frame because it cost in the 400 dollar land. ... Start with solid sheet and eliminate all the "pretties". ... Some of the guys designing this stuff need to get jobs outside of ...
    (rec.crafts.metalworking)