Active Clock Tuning (ACT) is a feature on the PIC16(L)F191XX family of devices. The ACT module works by continuously adjusting the High-Frequency Internal Oscillator (HFINTOSC), using an available external 32.768 kHz oscillator attached to the Secondary Oscillator (SOSC) pins to achieve ±1.0% clock accuracy. Since the PIC16(L)F191XX family does not support other external crystal modes, the ACT was added to remove the need for an external high-accuracy clock source. The increased accuracy of the ACT module is useful in serial communications like UART, SPI, and I2C.