Does Fosc refer to the crystal frequency before or after PLL is applied for PIC18 microcontrollers?

Question

If I have a PIC18 microcontroller with an 8MHz crystal and 4xPLL, is Fosc 8MHz or 32MHz?

Answer 1

F_osc is the clock eventually with PLL, so with an 8MHz crystal and 4xPLL you would have an F_osc of 32MHz. However, note that this is divided by 4 internally, so that you will be able to handle 8 million instructions per second (MIPS).

I found this in the 18F2520/2620/4525/4620 datasheet, table 17-3 on page 187. You can see that F_cy, the cycle frequency, equals F_osc/4. F_osc therefore has to be with PLL.