內部 INTOSC 有兩種震盪頻率可以選擇 : 4MHz (+-1%) and 37KHz,這兩個頻率由 PCON Register 的 OSCF 位元決定。 PIC16F627A Data Sheet Page 27.
另外要設定震盪器模式,這時就需設定 Configuration Words 的 <FOSC2:FOSC0> 的選項。這個選項可以在燒錄時透過 MPLAB IDE 的 Configuration Bits 選項設定或直接瘥城市裡設定。底下就是其選項: bit 4, 1-0: FOSC2:FOSC0: Oscillator Selection bits(4) 111 = RC oscillator: CLKOUT function on RA6/OSC2/CLKOUT pin, Resistor and Capacitor on RA7/OSC1/CLKIN 110 = RC oscillator: I/O function on RA6/OSC2/CLKOUT pin, Resistor and Capacitor on RA7/OSC1/CLKIN 101 = INTOSC oscillator: CLKOUT function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN 100 = INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN 011 = EC: I/O function on RA6/OSC2/CLKOUT pin, CLKIN on RA7/OSC1/CLKIN 010 = HS oscillator: High speed crystal/resonator on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN 001 = XT oscillator: Crystal/resonator on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN 000 = LP oscillator: Low power crystal on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN