DS3234 real time clock reset pin
The DS3234 has a reset/brownout detector circuit as needed for µCs without a brownout detect function. It monitors Vcc and checks whether it is higher than roughly 2.5V. If it's below, it holds the RST output low, if it's higher for 250ms, it releases the RST line, which is floating then. In addition, you can connect a push button to the RST line for manual reset, which starts the very same timer of 250ms on release.

You have to use the same Vcc for the µC and the DS3234 to make this work. If Vcc is below 2.5V, RST is not floating but pulled to GND then.

If you don't need this function, simply do not connect the RST pin.