The PIC18F458-I/PT is a high-performance Enhanced Flash Microcontroller with CAN module. The RC oscillator frequency is a function of the supply voltage, the resistor (REXT) and capacitor (CEXT) values and the operating temperature. In addition to this, the oscillator frequency will vary from unit to unit due to normal process parameter variation. The EC and ECIO oscillator modes require an external clock source to be connected to the OSC1 pin. The feedback device between OSC1 and OSC2 is turned off in these modes to save current. There is no oscillator start-up time required after a Power-on Reset or after a recovery from sleep mode. The PIC18F458 device includes a feature that allows the system clock source to be switched from the main oscillator to an alternate low-frequency clock source.