check ds1820 datasheet it´s a good source of information
http://datasheets.maxim-ic.com/en/ds/DS18S20.pdf

2011/3/19 Marc MERLIN <marc_n...@merlins.org>:
> On Sat, Mar 19, 2011 at 08:38:58AM +0100, Pascal Baerten wrote:
>> Hi Marc,
>> The protocol require that the master always initiate the communication. so
>> polling is unavoidable.
>> However the functinality you're wondering exist;  you may reduce bus traffic
>> by using alarm function:
>>
>> basically you configure the slave to respond to conditionnal search only
>> when a change occurred on its inputs.
>> on ds2408 use the set_alarm property to configure conditional behaviour. (
>> http://owfs.org/index.php?page=ds2408) then iteratively look for alarmed
>> slaves by enumerating devices of alarm directory and read bit state only on
>> theses alarmed devices.
>
> So, how does the master keep track of who triggered their alarm?
> Is it somehow quicker for the master to poll every device just for the alarm
> bit and it already does so every second or so, or in the case of alarm are
> the slaves able to send that bit?
>
>> while this polling does not seems effective when few slaves are monitored on
>> the bus, this become really interesting when many have to be monitored. you
>> are able to poll 10 time per second as many slave as the bus may hold.
>>
>> Adding the use of simultaneous property for temperature aquisition, and you
>> never lock the bus for duration of a conversion. even ds18?20 temp sensors
>> use alarm function to appears in alarm directory (after a conversion
>> command) if temp goes outside given limits.
>
> That's great to know, thank you.
>
> Marc
> --
> "A mouse is a device used to point at the xterm you want to type in" - A.S.R.
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> Home page: http://marc.merlins.org/
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