DS3231 purpose of 2 resistors?

In DS3231 datasheet there's a mention of 2 resistors (Rpu). What is the purpose of those and how do I determine value?
I know it says Rpu=Tr/Cb, but I couldn't find what those Tr and Cb means, which confused me even more :frowning:

They are pull up resistors for the I2C lines and they should both be 4K7.

Same for the pullups on INT/SW and 32KHz.

Ah right! It's been a while, I forgot those need pullups :slight_smile: Thanks!
One more question. Is it absolutely necessary to connect all NC pins to the ground?

Seeing as the data sheet says:-

All N.C. (no connect) pins must be connect- ed to ground.

Then I would say yes it is.

Grumpy_Mike:
Seeing as the data sheet says:-

All N.C. (no connect) pins must be connect- ed to ground.

Then I would say yes it is.

Ah, I must be blind, sorry about that, it is there in bold font too!
Thanks Mike!

It seems mad the 8 pin package is so hard to get when all the extra 8 pins on the 16 pin package are just grounded.

Riva:
It seems mad they no longer make the 8 pin package when all the extra 8 pins on the 16 pin package are just grounded.

Oh yeah good point, SO16 is what I can find anyway... BTW I can only find eagle library for SO16W (wide?) version. Is there much difference between SO16 and SO16W?

This 8 pin part?

The 16's only have 1 size listed on the datasheet.
16-SOIC (0.295", 7.50mm Width)