By default internal pull-up resistors for TWI SCL & SDA pins

[raccoon]

Why are the SCL and SDA pins by default (nRF SDK 11.0, nrf_drv_twi.c: 44-57) configured to use the internal pull-ups?

[rushin]

For I2C, SCL and SDA pin requires pull up. so it is configured to use internal pull ups. so you don't require external pull ups

[Ole Bauck]

@rushin: That is correct. However the internal pull ups (13Kohm) may be too weak to work for all configurations. Together with the pin capacitance (4pF) you will start having problems for TWI frequency of 400KHz. The lines will be skewed. At 100KHz it will work fine.

Generally, the pull up resistance on TWI is around 4.7K. If you have internal pull up resistors on the slave also it should work fine in most cases (13/2 = 6.5Kohm).

[Ole Bauck]

You want the option to turn on/off pull ups in the TWI configuration? This was added to the TWI slave driver. I can discuss internally if this should also be added to the TWI master driver.

[raccoon]

Maybe I need to clarify things. Since we have external pull-ups for the SDA and SCL lines (I understand that the internals are not an option) why would you want to also have the internal pull-ups enabled?

[raccoon]

I was successful in disabling the internal pull-ups (following this post). I was just wondering what are the consequences I will face, since Nordic must have a reason for enabling them by default.