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

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

MartinBL — Fri, 03 Feb 2017 15:52:47 GMT

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

Ole Bauck — Fri, 03 Feb 2017 12:52:05 GMT

There are no consequences in your case (as you might have figured out ;) ).

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

Ole Bauck — Fri, 03 Feb 2017 12:48:59 GMT

At 100 KHz internal pull ups will be fine. At 400 KHz the speed may become slower (depends on the total capacitance and resistance of the line) if only the internal pull up on the nRF is used, this is at least what we have seen if you connect the one nRF as TWI master and one nRF as TWI slave and only have internal pull up on one of the pins (the clock line became around 250 Khz or so). If internal pull up is enabled on both the master and slave, 400 KHz should work just fine. I will update my answer to be more precise.

Internal pull up something totally separate than the TWI peripheral. You can see the internal pull ups as a "hack" you can use to remove the external pull ups (and hence save board space and BOM).

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

raccoon — Fri, 03 Feb 2017 12:28:46 GMT

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.

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

raccoon — Fri, 03 Feb 2017 12:24:55 GMT

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?

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

Ole Bauck — Fri, 03 Feb 2017 10:04:09 GMT

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.

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

Ole Bauck — Fri, 03 Feb 2017 10:03:14 GMT

@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).

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

rushin — Fri, 03 Feb 2017 07:08:40 GMT

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