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XC2200 Derivatives
System Units (Vol. 1 of 2)
Architectural Overview
User’s Manual
2-32
V2.1, 2008-08
ArchitectureX22, V1.1
2.4
Clock Generation
The Clock Generation Unit uses a programmable on-chip PLL with multiple prescalers
to generate the clock signals for the XC2200 with high flexibility. The system clock f
SYS
is the reference clock signal, which can be output to the external system. The system
clock f
SYS
can be derived from several internal and external clock sources.
The on-chip high-precision oscillator (OSC_HP) can drive an external crystal or accepts
an external clock signal. The oscillator clock frequency can be multiplied by the on-chip
PLL (by a programmable factor) or can be divided by a programmable prescaler factor.
An internal clock source can provide a clock signal without requiring an external crystal.
The Oscillator Watchdog (OWD) supervises the input clock and enables an emergency
clock if the input clock appears as not reliable.