When accessing the I2C device connected to the Nordic controller nRF 52832, The CLK frequency changes during the process, resulting in operation at an unintended frequency.

[usuda]

(Overview)
When accessing the I2C device connected to the Nordic controller nRF 52832,
The CLK frequency changes during the process, resulting in operation at an unintended frequency.

(Hardware configuration)
bluetooth module : EYSHJNZXZ
chip : nRF52832
device : I2C device
   The connection with the chip is SCL P0.03, SDA P0.04, as standard SDK I2C sample source, the controller is connected. (\examples\peripheral\twi_master_with_twis_slave)

(software configuration)
SDK : Nordic SDK 12.3.0
F/W: Based on the SDK sample source (\ examples \ ble_peripheral \ ble_app_uart),
       Added I2C access processing.
   -In the I2C access processing, necessary functions are added with reference to the SDK sample source. (\examples\peripheral\twi_master_with_twis_slave)
   -The I2C frequency remains as the sample source.(400khz)

(Symptom details)
 With I2C access,
   At the time of transmission (address, command) from the master (nRF 52832), it operates as intended at CLK 400 kHz
   At the time of reception (data) from the slave (I2C device), it becomes CLK 200 kHz and unintended operation takes place.

(question)
Please tell me about the causes and countermeasures of CLK frequency change during I2C access.

[Håkon Alseth]

In addition to Keton's comment, you'd need stronger pull resistors when operating at 400 kHz. See more info on that here: http://dsscircuits.com/articles/effects-of-varying-i2c-pull-up-resistors

Rpull of between 2.2k and 4.7k should provide nicer looking rise-times.

Cheers,

Håkon