Re: [PATCH] gpio: max732x: add support for MAX7319, MAX7320-7327 I2C Port Expanders

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

On Sun, 13 Jul 2008 02:12:36 -0700, David Brownell wrote:
> > 3. for chips like max732x, actually, the range of 0x50 - 0x5F will be
> > monitored by the I2C chips at startup to decide the connections of
> > AD2/AD0 pins to GND/VCC/SCL/SDA,
> 
> There's no need to monitor addresses ... before the first data bit
> is sent -- whatever value! -- it's known how those pins are wired:
> 
>  - START bit ... SCL is high, SDA falls.  Any pin that stayed
>    low is wired to ground.  Any pin that changed high-to-low is
>    thus connected to SDA.
> 
>  - Prepare to send first bit ... SDA still low, SCL falls.  Any
>    pin that stayed high is wired to Vcc.  Any pin that changed
>    high-to-low is connected to SCL.
> 
> And then the master updates SDA to match the first (address) bit,
> and lets SCL be pulled high ... the i2c slave has all the data it
> needs to be able to determine its address.

Totally true. Add to this that the first 3 address bits can't change,
this gives the chip some more time to setup its internal logic to match
the 4 LSBs by the time they come.

-- 
Jean Delvare

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