I2C frequencies below 100kbps

RE: I2C frequencies below 100kbps

cellular_iot — Mon, 17 Nov 2025 12:03:30 GMT

oh thanks, this is really working!!!

RE: I2C frequencies below 100kbps

AlanIoT — Tue, 24 Sep 2024 11:57:31 GMT

I had read multiple forum posts looking for a solution to the same problem, before giving up. Later I stumbled onto this post, which explains a very easy hack to set the bitrate lower than 100kbps (Thank you Burt !)

Under `toolchainVersion > modules > hal > nordic > nrfx > mdk > nrf9160_bitfields.h` you can find the line

#define TWIM_FREQUENCY_FREQUENCY_K100 (0x01980000UL) /*!< 100 kbps */

Simply changing this value according this instruction was the solution to our problem. So I set the value to 10 kbps

#define TWIM_FREQUENCY_FREQUENCY_K100 (0x0028F000UL) /*!< 100 kbps */

and here you can see that the SCL ticks are 100 µs long and the sensor responds now.

We are reading a sensor hanging on an 8 meter long cable, which is impossible without lowering the bitrate to a much lower value.

RE: I2C frequencies below 100kbps

Turbo J — Sat, 07 Jan 2023 23:08:16 GMT

Nope - if your read the PS, those constants are the only values that the hardware supports. The 100kBps is the minimum.

However, the hardware supports clock stretching. That could help you in some cases depending how much control you have over the slave.