A fixed prescaler is fixed, thus and can´t be "set". Some microcontroller have, some don´t. I´m not familiar with your microcontroller. Read the datasheet.
A fixed prescaler is fixed, thus and can´t be "set". Some microcontroller have, some don´t. I´m not familiar with your microcontroller. Read the datasheet.
I can´t answer without reading the datasheet.
I tried, but now I recognize that in the headline you talk about PIC18F45k80, but the uploaded page is from PIC18F66K80.
So I opened PIC18F66K80 datasheet...and Fig. 13-1 and Fig. 13-2 clearly shows "Fosc/4" as clock input. Which is a fixed 1:4 divider.
Fosc never - undivided - comes to the counter.