This slide presents an overview of the FR59xx family clock system. The main advantage of the orthogonal FR59xx clock system is its ability to branch any clock source to any system clock. There are two external and three internal clock sources. The external clock sources are: A low frequency crystal oscillator - typically 32768 Hz for the RTC and a High frequency crystal oscillator with a frequency limit between 4 and 24 MHz. The internal clock sources include the VLO: a very low power, low frequency internal oscillator that operates at approximately 10 kHz the DCO a high frequency digitally controlled oscillator with factory calibrated frequencies and the MODOSC a 5 MHz oscillator used internally for peripherals such as the ADC. These clocks can be used to source the CPU clock also known as main clock or MCLK, the high speed peripheral clock also known as sub-main clock or SMCLK and the auxiliary clock or ACLK. The default startup frequency for the system is 1 MHz sourced by the DCO.