[i2c] Using 2 identical chip i2c device in the same bus

Arnold abo_gwapo at yahoo.com
Wed Nov 22 11:19:50 CET 2006

Hi Jean,

Thank you for taking time to read my mail and also
Thanks for your suggestion. I would try both your
suggestion and the multiplexer. Just a quick question
-- After I configure the multiplexer, could already do
the routine for the sensor attach as if it is not
connected to multiplexer?

--- Jean Delvare <khali at linux-fr.org> wrote:

> Hi Arnold,
> On Tue, 21 Nov 2006 17:56:28 -0800 (PST), Arnold
> wrote:
> > I've been stuck with the problem of having 2 i2c
> > device on 1 bus line. And I have learned that you
> can
> > not attach 2 same device to 1 bus line because of
> the
> > addressing. To solve this problem I attached a
> > 2-channel i2c multiplexer. 
> This isn't entirely true. Many chips can be
> configured to use
> different addresses, by wiring one or more dedicated
> address pins to
> the ground, VCC, or left floating. For example, the
> LM83 has 2 3-state
> address pins, so you can wire up to 9 such chips on
> the same bus. Some
> chips don't have address pins but several variants
> can be purchased,
> each with a different address. For example there are
> two variants of
> the ADM1032 chip, one with address 0x4c and one with
> address 0x4d.
> > Does anybody have used a PCA9540B 2-channel i2c
> > multiplexer? If yes, could you give me a hand on
> how
> > it works? or if you could share the steps on how
> to
> > configure this? 
> There is a test driver in the lm_sensors source
> package
> (kernel/chips/pca9540.c), but proper support for
> multiplexed busses is
> still missing. So I strongly advise that you simply
> choose chips that
> can use different addresses and don't bother with
> multiplexing.
> -- 
> Jean Delvare

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