Re: [Xml1-wire-devel] New hub design, request for input

[Bruce B. <bb...@sy...>]

At 00:40 1/19/2001 +0100, Jac Kersing wrote:
>On Thu, 18 Jan 2001, Bruce Boyes wrote:
>
>> One thing we have been tipped off by Dallas about is that if you short an
>> active branch on the 2409 it will hang the network and the 2409 can't
>> recover except by power cycling. This is a bug in the 2409 design which
>> isn't likely to change soon.
>
>That's the end of my access control design. One can't rely on users to
>slot their iButtons into the reader (the one with led) without causing a
>short every now and then. Back to the drawing board :-(

Wait! I didn't mean to paint so dark a picture. The other end of the
equation is that the DS2409 will reset itself turning off both branches
*after* the short ends. So in the case of an accidental reader short you're
OK. In the case of vandalism or physical damage to one branch (fire melts
one end into a lump or someone crushes a cable) which causes an eternal
short, you're stuck unless you can power cycle the 2409 and thereby disable
that branch.

The same short on the trunk due to gross events such as a fire, etc will of
course bring down the net, but that would also cause any other network to
fail too.

>
>> So we are pondering a watchdog which would power cycle the 2409. When the
>> 2409 is power  cycled it disabled both branches.
>
>What about a watchdog that resets the 2409 whenever the active branch is
>short? If the one-wire signal level stays below a threshold for over 1
>second just reset the part. This way there would be no need for almost
>continues one-wire activity.


Yes! Dave at Dallas suggested the same thing.

Bruce
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