NRF52832 and DS3231 RTC - question about using 32KHz as LFXO

[polynomialtime]

Hi I'm considering a design with this precision RTC

I intend to use the 32KHz output on XL1 (and XL2 grounded) as I've seen done here, but the DS3231 datasheet says the 32KHz is an open drain that needs a pull-up resistor, so do I need a resistor even when I'm using it as LFXO?

[RK]

Don't see how it's going to work if you don't install one. Although the description of XL1/XL2 used with an external signal is a bit lacking in detail (eg what a 'low' signal means and what the input impedence is) just connecting an open drain to an input buffer is going to result in nothing more than a bit of noise around 0V, if even that. You're going to need a pullup to actually get the voltage to swing. 

Apart from that, if you're doing the design, just design for a pullup resistor, if you find (unlikely) that you don't need one, just leave it N.C.

[polynomialtime]

Ok that's what I was leaning towards but thanks for confirming since as you say documentation on this is pretty lacking