Subject:
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Re: Brainstorms
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 13 Aug 2002 23:54:42 GMT
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Viewed:
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950 times
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In lugnet.robotics, sjbaker1@airmail.net writes:
> Wayne Gramlich wrote:
>
>
> > That is only a partial bus scan. It does not tell you what is at
> > each address.
> >
> > A full bus scan allows people to plug arbitrary devices into the bus
> > and allows the bus master to to reliably figure out what has been
> > plugged in and where. Bus conflicts are either designed out or
> > detectable.
> >
> > It is fairly easy to find out what addresses are occupied on an I2C
> > bus. Address conflicts may be detectable, but I sure do not know
> > how it is done. Figuring out whether the user plugged in a serial
> > EEPROM, an A/D, or another microcontroller is the far harder task
> > to solve. Again, I'm not saying it can't be solved, but until
> > someone really articulates how they plan on pulling it off, I will
> > remain skeptical of people who claim it is easy.
>
> I thought Philips kept a master registry of all the hardwired I2C
> addresses allocated to each chip vendor? That should mean that just reading
> the hardwired address is enough to tell you what *kind* of device you've
> found.
There are only 1024 maximum addresses. There are more than
1024 I2C chips out there. Ergo, there are address conflicts
between some of the chips out there.
Unfortunately, there is no requirement that 2 chips at the
same address implement the same commands. Thus, there is
no real way to figure out what you have. Indeed, there are
some chips from the *same* vendor that have address conflicts
and do not implement the same commands.
Contrast this with RoboBricks where every RoboBrick module
must implement the same 8 shared commands. Two of these
comands are used to read identification information out
of the RoboBrick.
It would be nice if Philips had thought ahead and put
some mandatory identification commands into all chips,
but they did not. Too bad. Boo hoo. It might be
possible to figure out which chip is occupying a given
address slot, but it sure won't be easy.
-Wayne
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Message has 1 Reply:
 | | Re: Brainstorms -- A Simple Unique Addressing Scheme
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| There's been a lot of messages on how to determine unique addressing for intelligent peripherals. Model railroading has solved this problem in a fairly easy way. THe NMRA (National Model Railroading Association) defined the DCC (Digital Command (...) (22 years ago, 14-Aug-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Brainstorms
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| (...) I thought Philips kept a master registry of all the hardwired I2C addresses allocated to each chip vendor? That should mean that just reading the hardwired address is enough to tell you what *kind* of device you've found. ---...--- Steve Baker (...) (22 years ago, 13-Aug-02, to lugnet.robotics)
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