DSPIC33 MCU oscillator - PLLDIV setting issue
Posted: 03 Feb 2019 15:06
Hi all,
In my project I am using a DSPIC33EP512MU810 with 8MHz XTAL and PLL by setting N1=2, N2=2 and PLLDIV=38 (M=40) thus complying with oscillator setting specifics and getting, as expected, a correct Fosc of: 8 * (M / N1*N2) = 80 MHz.
Then I've changed the XTAL to a 16Mhz and changed the PLLDIV to 18 (M=20) that is also complying with the specifics, and expected to get the same Fosc of 80 MHz, but instead I found that Fosc becomes apparently doubled (160MHz) and I can't understand why, since doubling XTAL frequency and at the same time halving the M multiplier should result in the same Fosc as before, but it isn't working this way for me.
Please note that I didn't do an actual MCU clock frequency measurement, but just observed that a led blink test, before and after the XTAL change, shows a doubled blinking frequency.
Did anyone deal with the same issue and can suggest an explanation / solution?
Thanks a lot in advance!
Roberto
In my project I am using a DSPIC33EP512MU810 with 8MHz XTAL and PLL by setting N1=2, N2=2 and PLLDIV=38 (M=40) thus complying with oscillator setting specifics and getting, as expected, a correct Fosc of: 8 * (M / N1*N2) = 80 MHz.
Then I've changed the XTAL to a 16Mhz and changed the PLLDIV to 18 (M=20) that is also complying with the specifics, and expected to get the same Fosc of 80 MHz, but instead I found that Fosc becomes apparently doubled (160MHz) and I can't understand why, since doubling XTAL frequency and at the same time halving the M multiplier should result in the same Fosc as before, but it isn't working this way for me.
Please note that I didn't do an actual MCU clock frequency measurement, but just observed that a led blink test, before and after the XTAL change, shows a doubled blinking frequency.
Did anyone deal with the same issue and can suggest an explanation / solution?
Thanks a lot in advance!
Roberto