Hello,
The resistor is intended to restrict charge current, if chargeable battery is applied:
“Appropriate series resistor (Rs) must be used when connecting the coin cell. Rs depends
on the charge current limit that depends on the chosen coin cell.”
Refer to section, named OSC32K in i.MX 6UL Datasheet(s), for more details.
https://www.nxp.com/docs/en/data-sheet/IMX6ULCEC.pdf
So, the Rs resistor may be removed if non- chargeable battery is used in Your design.
Note, if diode D2 is used, R1 resistor is not required and vice versa.
Have a great day,
Yuri
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