2010/1/29 Sophana K <[email protected]>
> Hi
>
> >From the ds2409 description:
> >>>>
> the coupler maintains a common ground level for the whole network and
> keeps the inactive segments powered. This simplifies supplying central
> or local power for additional circuitry and prevents loss of status of
> parasitically powered devices. It also avoids disrupting communication
> caused by the parasitic power supply of 1-Wire devices after
> activating a branch.
> <<<<
>
> It appears that the ds2409 is designed to help parasitically powered
> devices doing their job while other branches are accessed.
> It could mean that each ds2409 branch could be considered totally
> independant.
>
> DS2409 does not provide a strong pullup on unselected branches (pullups is
1.5k ohm -> max 3.3 mA supplied.)
So to is correct as long as no more than 2 parasitical temp chips are
presents. (ds18b20 chips consume up to 1.5 mA during conversion)
But after reading the ds2409 datasheet, there is something I don't
> understand, there is a direct-on main command but no direct-on aux
> command. Should I understand that everytime a branch is accessed, a
> reset pulse is sent first? meaning that it is not possible to access
> other branches while an unpowered conversion?
>
> direct-on-main allows to access main branche as if it was directly
connected to the 1wire bus (bypassing indirect addressing via the hub)
Every rom commands are preceded by a reset pulse, this does not impact
unpowered conversions as long as the branch is not selected.
in the other thread, daryl said:
> >>>>>>
> I just tried it by adding an unpowered sensor to my net and doing the
> following...
>
> echo 1 > simultaneous/temperature
> cat 10.*/temperature
>
> The result was that it paused to do the conversion on the one
> unpowered sensor, and all the powered ones came up right away. The
> unpowered sensor probably tries to do the conversion with all the
> powered ones, but since the data bus isn't being held high the
> conversion fails.
> <<<<<<<<<<
> I think the explaination of this is that the unpowered device lost its
> power because of the data line not being held high by the strong
> pullup.
> As it totally lost power, it goes into unknown state, and can't
> respond to new convert commands before being initialized again.
>
> So it is true that powered and unpowered should not be mixed only in a
> branch.
>
> In my system, unpowered devices are all in separate branches, and I
> should be able to make simultaneous conversions.
>
> True as long as you provide enough power on that branch (maybe adding an
external pullup).
Also, I don't understand how jerry's example works. He triggers the
> top simultaneous temperature reading. Does this trigger the conversion
> on all hub branches?
>
> When root simultaneous/temperature is triggerd, I think that owfs loop on
all branches sequentially
>
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--
Pascal
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