NRF52832 TWI at 50 KHz (SMBus Compatibility)

[Greg Nowak]

I am running the NRF52832 (BMD-300 module) and I'm trying to talk to battery over SMBus. SMBus is compatible with devices up to 100 KHz.

I was wondering if there was a way to talk to an I2C device on the NRF52832 with a lower clock rate than the 100 KHz rate given in the TWI library.

I see here that the frequency is not configurable beyond 3 predefined clock rates, 100K, 250K, and 400K. infocenter.nordicsemi.com/index.jsp

What I'm experiencing is inconsistent readings between my battery and board. I have about a 60% success rate when reading. The battery manufacturer stressed that I need to be SMBus compliant, not just I2C. They suggested that I use a slower clock rate than 100 KHz.

I was wondering if anyone out there knew if it was possible to use a slower clock rate for I2C communication using the NRF52832?

Thanks,

Greg

[embeddedER]

Hi Greg,

Were you able to make nRF52 work with 50k? I've sensor which is using bit-bang I2C and it's rate is much slower (~50k).

Could you please share the sample if it worked for you?

Thanks.

[Greg Nowak]

I just changed the timing register to 0xCC0000 in order to communicate with my smart battery and that seemed to work. 
Technically it is 'outside of the tested specification" but I've got hundreds of products so far with this change and I haven't had any issues yet.  

[embeddedER]

Thanks Greg for quick revert. I am new to nRF devices, nRF SDK and still consuming lot of information.

Could you share the snippet of code (or guide me) on "how to set FREQUENCY register" in my application?

TIA.

[embeddedER]

To make myself more clear:

I am using nRF Connect SDK 1.8.0 and I changed the register (TWIM_FREQUENCY_FREQUENCY_K100) value in nrf52_bitfields.h and it worked for me.

But this change is outside my application i.e. if I migrate to latest SDK later on then I'll need to do change in that SDK as well. So, I was just wondering if there is a way to change this register from my application itself?

Thanks.

[Greg Nowak]

Not that I have found.  I keep it in my repo as my "things to change when I upgrade" list.  I've just manually updated each time I update (which, admittedly is not very often)