Overview
The FM31xxx and FM33xxx are integrated processor companion devices that feature a real-time clock or RTC. The RTC provides the date or time information for the system and operates on either VDD or VBAK (battery) power. The RTC oscillators in FM31256 and FM3164 are designed to use a 6 pF crystal; however, you can use the more common 12.5 pF type if you consider the implications. This application note focuses on the use of 6 pF vs. 12.5 pF crystals for the RTC oscillator designed for 6 pF.