840 twi driver problem

RE: 840 twi driver problem

William.wei — Thu, 11 Jan 2024 07:51:52 GMT

Thanks Kenneth，

I have shared your information to customer and solved this problem.

thanks again!

Regards,

William.

RE: 840 twi driver problem

Kenneth — Wed, 10 Jan 2024 10:57:49 GMT

[quote user="William.wei"]could you please send me your case, and i can see it for more information.[/quote]

Not if it's much useful to look at the other case, but here it is:
https://devzone.nordicsemi.com/support/319995

[quote user="William.wei"]

so may i ask if we have and workaround for 400khz twi clk in this case?

[/quote]

If you can't change the design: You can use 250kHz, or you need to reduce the pull-up resistors. At least for test I suggest to try a very small pull-up resistor (e.g. 1kohm) just to confirm that the frequency increase to 400kHz again.

Kenneth

RE: 840 twi driver problem

William.wei — Wed, 10 Jan 2024 04:54:08 GMT

Thanks Kenneth,

could you please send me your case, and i can see it for more information.

the good news is 250k still works, and the difficult point is customer hardware is ready for production.

so may i ask if we have and workaround for 400khz twi clk in this case?

Regards,

William.

RE: 840 twi driver problem

Kenneth — Mon, 08 Jan 2024 11:04:28 GMT

Hello,

I saw a similar case the other day. I have some suggestion, and I also have a theory of the problem.

The rise time you see directly depend on the capacitance on the lines and the pull-up resistor. If you have more devices connected on the i2c lines this will increase the capacitance on the lines, and thereby increase rise time. If you reduce the pull-up resistor this will reduce the rise time.

What I think happens here is that the rise time is so slow, that the hardware interpret it as clock stretching occurs by the slave(s), in this case the hardware may wait one clock cycle before it continue to clock next bit. I suspect this may half the the frequency in worst case, I guess the solution to this is either reduce pull-up resistor, or place some of the devices on different pins.

Kenneth