I2C fast mode frequency

RE: I2C fast mode frequency

Kirk Wayland — Fri, 01 Aug 2025 21:52:08 GMT

413Khz produces pulse width's of 1.21 usec, a problem for LOW SCK duration. Min for SCK is 1.3 usec.

Spec is spec, so having timing that violates spec is not a good idea whether or not it works on your bench.

RE: I2C fast mode frequency

CheMax — Mon, 07 Feb 2022 13:25:32 GMT

sorry, I just passed by. And it seems to me that you do not understand each other. I'll rephrase the question a little. the question is not whether the NRF can support a speed of 250 kHz, but how to set the desired speed using the Zephyr.

for some unknown reason, Zephyr for this board suggests using the i2c module and offers constants for 100 kHz, 400kHz and 1000kHz. but for NRF it is more correct to use the TWIM module.

I understand that the topic starter's question is exactly this: how to switch to TWIM in Zephyr and set the speed to 250 kHz, aren't?

[quote userid="106849" url="~/f/nordic-q-a/84201/i2c-fast-mode-frequency/351410#351410"]as i mentioned earlier in this link https://docs.zephyrproject.org/latest/reference/peripherals/i2c.html while developing on zephyr I2C defined speed configurations we have definition for mentioned speed only[/quote]

You shouldn't use I2C. You must change using node to TWIM (Please, read this page: https://docs.zephyrproject.org/latest/reference/devicetree/bindings/i2c/nordic%2Cnrf-twim.html#dtbinding-nordic-nrf-twim). and after this. you can use speed 250kHz.

RE: I2C fast mode frequency

Priyanka — Mon, 07 Feb 2022 12:38:13 GMT

Hi Hitesh,

As you can see from the TWI documentation,

The speed 250kbps is supported and this should be the default speed if no speed configuration is mentioned.

Regards,

Priyanka

RE: I2C fast mode frequency

hiteshk014 — Fri, 04 Feb 2022 22:47:36 GMT

Hi,

as i mentioned earlier in this link https://docs.zephyrproject.org/latest/reference/peripherals/i2c.html while developing on zephyr I2C defined speed configurations we have definition for mentioned speed only

I2C Standard Speed: 100kHz - I2C_SPEED_STANDARD
I2C Fast Speed: 400kHz - I2C_SPEED_FAST
I2C Fast Plus Speed: 1MHz - I2C_SPEED_FAST_PLUS
I2C High Speed: 3.4MHz - I2C_SPEED_HIGH
I2C Ultra Fast Speed: 5MHz - I2C_SPEED_ULTRA

can you please suggest if we are to use nrf connect sdk how do we add configurations for 250khz as existing configurations are only for mentioned speed.

Thank you,

RE: I2C fast mode frequency

Priyanka — Tue, 01 Feb 2022 16:02:32 GMT

Hi Hitesh,

As CheMax mentioned, 413kHz should be fine as it's just a slight variation. And regarding the i2c speeds, since the BL653 has the nRF52833, you should be able to use the 250kHz speed, as mentioned, in nrf-twim.

Regards,

Priyanka

RE: I2C fast mode frequency

hiteshk014 — Tue, 01 Feb 2022 09:36:13 GMT

Hi Nordic Support,

We are waiting for your response.

RE: I2C fast mode frequency

hiteshk014 — Sun, 30 Jan 2022 12:53:41 GMT

Thank you for response Chemax,

will wait for support service to acknowledge.

RE: I2C fast mode frequency

CheMax — Sat, 29 Jan 2022 13:47:12 GMT

Hi,

[quote userid="106849" url="~/f/nordic-q-a/84201/i2c-fast-mode-frequency/350310#350310"]can you please provide input to query number 2 of I2C speed modes,[/quote]

seems I understand what the question is.

Zephyr for this board (BL653) suggests using the I2C driver. while for nordic chips, in the same document there is a reference to the use of TWI, when setting which you can explicitly specify the exchange rate in Hz (see here nrf-twim with zephyr).

Unfortunately, I have practically no experience in working with Zephyr , so if you still have questions, clarify them and wait for a response from the support service.

best regards,

RE: I2C fast mode frequency

hiteshk014 — Sat, 29 Jan 2022 13:01:06 GMT

Hi CheMax,

Thank you very much for quick response,

can you please provide input to query number 2 of I2C speed modes,

Regards,

Hitesh

RE: I2C fast mode frequency

CheMax — Sat, 29 Jan 2022 09:38:51 GMT

short answer:
There is nothing wrong with that, the device will work.

and yes, the "Fast +" mode is used only in nrf5340. otherwise only have "standart" and fast modes this is due to the fact that for high exchange frequencies, current control of the lines is already required in order to obtain steep fronts.

more expanded:
The standard does not define the bus rate, but rather simply specifies the typical times: low clock duration, clock high duration, and rise time. These parameters add up the exchange rate, but you noticed that the speed is indicated not in bits / s, but in Hz.
therefore, for a typical speed of 400 kHz, a small variation is allowed. the main thing is to monitor the steepness of the fronts and the capacity of the bus. Capacitance for 400 kHz should not exceed 400 pF. It is better to generally be at the level of 100-200 pF.
also, the fact that you measured 413kHz does not mean anything, since the next data frame may have a different frequency. this is due to the fact that, by default, nrf52 chips clock the peripherals from an internal source. if you switch forcibly to an external quartz resonator / oscillator, you will get different numbers.

p.s. see you diagrams in analog mode. then you will see if the pull-up resistors have been chosen correctly.

from what I see, I suspect a very weak leading edge. Due to this, the clock pulses are quite narrow.

and yes, the frequency meter from sale is mediocre. it counts at the level of 0.7 from the one specified in the settings. therefore, often the readings also depend on the selected sampling frequency.