Good day all mighty experts,
So I picked up a couple of different ARM Cortex processors. Up until now, I have only dealt with the 8-bit AVR based controllers. But I feel I'm now ready to move onto some bigger 32-bit processors. I've got some small 32-pin TQFP Cortex-M0 processors to get started with ARM. However, for a larger future project, I also got a beefier Cortex-M4 SAM 4E. Now the biggest reason I picked this processor is because it has a maximum frequency of 120 MHz.
So what I am used to with AVR based processors (mainly the 644p DIPs) is connecting an external crystal clocked to the maximum frequency of the processor (20 MHz for the 644p).
On to the actual question... I have been reading more into the datasheet for the SAM 4E, and I see that it has a PLL, which I am hoping that you guys could help to confirm that I am understanding it correctly. So the processor has a 4, 8, or 12 MHz oscillator. From my understanding of reading about the PLL, it has a multiplier and a divider in order to set the desired clock frequency. I am unsure yet of the specific values that can be set for multiplier and divider (I have not dived into the registers yet), but is it correct to say that the multiplier can be set to say 10 and the divider to 1 along with the oscillator set to 12 MHz in order to achieve a frequency of 120 MHz, without an external crystal or oscillator?
If my understanding of that is all correct, under System Features of the datasheet, it says "One PLL up to 240 MHz for Device Clock and for USB," does this also mean the processor can achieve 240 MHz frequency by using a multiplier of 20?
So my question really is, can I achieve the maximum frequency of 120 MHz without utilizing an external crystal or oscillator?