TWI clock stretching for nrf51822

RE: TWI clock stretching for nrf51822

haruthakop — Fri, 18 Sep 2015 10:21:31 GMT

Hi thanks for your help.

Software controlled TWI Master driver supports bit and byte level clock stretching (It can be clearly seen from source code). I tested both (Software controlled and TWI hardware) implementations by delaying ACK bit, both were working.

Thanks again for your help.

RE: TWI clock stretching for nrf51822

MartinBL — Thu, 17 Sep 2015 10:51:11 GMT

I guess you can test it using a device which only tolerates low clock speeds, e.g. 100 kHz. Then you can try to run the TWI on your nRF51 at 400 kHz and see how the slave behaves. I actually concluded it works based on an unrelated test I have done and a brief talk with the TWI designer (who hadn't tested bitwise stretching specifically). What I did was actually testing what would happened if I used too large pullup resistors on the TWI lines. More specifically, what would happen if you only used the nRF51's internal 12 kOhm pullup resistors. What happened was that the device was not able to drive the lines as fast as I wanted and reduced the clock speed from 400 to 200 kHz (basically stretching the clock signals) due to slow rise times on the TWI lines. Except from the reduced clock speed it worked fine, so I concluded that bitwise clock stretching works.

RE: TWI clock stretching for nrf51822

haruthakop — Wed, 16 Sep 2015 14:13:08 GMT

Hi, Thanks a lot for your help. How did you test it? I also want to test it. Currently as a I2C slave I'm using an EEPROM. Do you have any idea how can I test bit level stretching with EEPROM?

Thanks again

RE: TWI clock stretching for nrf51822

MartinBL — Wed, 16 Sep 2015 09:05:12 GMT

Hi. I tested it and it seems to work. I agree that we should have better documentation on this.