AN2027 - PSoC® 1 - 32.768-kHz External Crystal Oscillator

Many microcontroller applications require a timing source more accurate than the typical internal oscillator. An external crystal can provide a solution. These crystals are used with an external crystal oscillator (ECO) to generate clocks as accurate as ±50 parts per million. PSoC^® 1 can implement an ECO that uses a 32.768-kHz crystal.

PSoC 1 microcontroller’s external crystal oscillator (ECO) can be used as a reference for timekeeping and other lowspeed (<32 kHz) operations. It can also act as the reference for the phase-locked loop (PLL) mode of the internal main oscillator (IMO). The PLL uses the 32.768-kHz input to generate a more accurate 24-MHz clock signal. This is used for operations that require an accurate high-speed clock such as dual-tone multi-frequency (DTMF) signal generation, serial communications, and RTC. Optimal performance from the ECO for each of these functions requires different external components and control register settings.