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XC2200 Derivatives
System Units (Vol. 1 of 2)
System Control Unit (SCU)
User’s Manual
6-14
V2.1, 2008-08
SCU, V1.13
6.1.4.6
Switching PLL Parameters
The following restriction applies when changing PLL parameters inside the PLLCON0 to
PLLCON3 registers:
•
The VCO bypass switch may be used at any time, however, it has to be ensured that
the maximum operating frequency of the device (see data sheet) will not be
exceeded.
•
Prescaler Mode should be selected.
•
After switching to Prescaler Mode, NDIV and PDIV can be adjusted.
•
Before deselecting the Prescaler Mode, the RESLD bit has to be set and then the
VCOLOCK flag has to be checked. Only when the VCOLOCK flag is set again, the
Prescaler Mode may be deselected.
•
Before changing VCOSEL, the Prescaler Mode must be selected.
Note: PDIV and NDIV can also be switched in Normal Mode. When changing NDIV, it
must be regarded that the VCO clock
f
VCO
may exceed the target frequency until
the PLL becomes locked. After changing PDIV or NDIV, it must be waited for the
PLL lock condition. This procedure is typically used for increasing the VCO clock
step-by-step.