On Fri, Dec 23, 2016 at 2:09 PM, M'boumba Cedric Madianga
<cedric.madianga@xxxxxxxxx> wrote:
> 2016-12-22 20:11 GMT+01:00 Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>:
>> On Thu, Dec 22, 2016 at 02:35:02PM +0100, M'boumba Cedric Madianga wrote:
>>> @@ -337,6 +350,16 @@
>>> slew-rate = <2>;
>>> };
>>> };
>>> +
>>> + i2c1_pins_b: i2c1@0 {
>>> + pins1 {
>>> + pinmux = <STM32F429_PB9_FUNC_I2C1_SDA>;
>>> + drive-open-drain;
>>> + };
>>> + pins2 {
>>> + pinmux = <STM32F429_PB6_FUNC_I2C1_SCL>;
>>> + };
>>
>> the second doesn't need the open-drain property? Why?
>
> I thought that open-drain was only needed for SDA line.
> But after double-checking I2C specification, it seems that SDA and SCL
> lines need open-drain or open-collector to perform the wired-AND
> function.
I think I2C SDA/SCL must be open drain by definition.
It also requires pull-up resistors, I guess you have these mounted on the board
so you do not need pull-up from the pin controller?
Yours,
Linus Walleij
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