The recommended crystal oscillator frequency for the DS3234S is 32.768 kHz.
The time can be set on the DS3234S by writing to the hour, minute, and second registers (0x02-0x04) using the I2C interface.
The internal oscillator of the DS3234S has an accuracy of ±2 ppm from 0°C to 40°C, and ±3 ppm from -40°C to 85°C.
Yes, the DS3234S can be used as a battery-backed RTC. It has a built-in battery switch and a battery monitor, and can automatically switch to battery power when the main power supply fails.
The DS3234S can be reset by writing 0x58 to the control register (0x0E). This will reset the RTC to its default state.