Frequency Modulated Phase Locked Loop and System Clocks (FMPLL)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
11-26
Freescale Semiconductor
2. Change the following in FMPLL_SYNCR:
a) Make sure frequency modulation is disabled (FMPLL_SYNCR[DEPTH] = 00). A change to
PREDIV, MFD, or RATE while modulation is enabled invalidates the previous calibration
results.
b) Clear FMPLL_SYNCR[LOLRE]. If this bit is set, the MCU goes into reset when MFD is
written.
c) Initialize the FMPLL for less than the desired final system frequency (done in one single write
to FMPLL_SYNCR):
– Disable LOLIRQ.
– Write FMPLL_SYNCR[PREDIV] to a desired final value.
– Write FMPLL_SYNCR[MFD] to a desired final value.
– Write the RFD control field value to a desired final RFD value + one.
3. Wait for the FMPLL to lock by monitoring the FMPLL_SYNSR[LOCK] bit. Refer to
Section 11.3.1.1, “Synthesizer Control Register (FMPLL_SYNCR)
,” for memory synchronization
between changing FMPLL_SYNCR[MFD] and monitoring the lock status.
4. Initialize the FMPLL to the desired final system frequency by changing FMPLL_SYNCR[RFD].
The FMPLL does not need to re-lock if only the RFD changes, and the RFD must be set to greater
than one to protect from overshoot.
5. Reenable LOLIRQ.
NOTE
When using crystal reference mode or external reference mode, do not set
the PREDIV value to any value that causes the phase/frequency detector to
go below 4 MHz. That is, the crystal or external clock frequency divided by
the PREDIV value must be in the range of 4–20 MHz.
NOTE
This first register write causes the FMPLL to switch to an initial system
frequency which is less than the final one. Keeping the change of frequency
to a lower initial value helps minimize the current surge to the external
power supply caused by the change in frequency. The last step changes the
RFD to get the desired final frequency.
NOTE
Changing the MFD or PREDIV values causes the FMPLL to perform a
search for the lock frequency that results in the system clock frequency
changing rapidly across the complete frequency range. All MCU
peripherals, including the external bus are subjected to this frequency
sweep. Operation of timers and serial communications during this search
sequence produces unpredictable results.
Summary of Contents for MPC5565
Page 18: ...MPC5565 Microcontroller Reference Manual Devices Supported MPC5565 MPC5565 RM Rev 1 0 09 2007...
Page 34: ...MPC5565 Reference Manual Rev 1 0 Freescale Semiconductor 15...
Page 35: ...MPC5565 Reference Manual Rev 1 0 16 Freescale Semiconductor...
Page 553: ...Flash Memory MPC5565 Microcontroller Reference Manual Rev 1 0 13 38 Freescale Semiconductor...
Page 559: ...SRAM MPC5565 Microcontroller Reference Manual Rev 1 0 14 6 Freescale Semiconductor...
Page 973: ...Preface MPC5565 Microcontroller Reference Manual Rev 1 0 21 36 Freescale Semiconductor...
Page 1153: ...Calibration MPC5565 Microcontroller Reference Manual Rev 1 0 B 8 Freescale Semiconductor...