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Device Clocking
RTC_XO pins. RTC core (CV
DDRTC
) must be powered all the time but the 32.768-KHz crystal can be
disabled if CLKIN is used as the clock source for the DSP. However, when the RTC oscillator is disabled,
the RTC peripheral will not operate and the RTC registers (I/O address range 1900h - 197Fh) will not be
accessible. This includes the RTC power management register (RTCPMGT) which controls the
RTCLKOUT and WAKEUP pins. To disable the RTC oscillator, connect the RTC_XI pin to CV
DDRTC
and
the RTC_XO pin to ground.
The USB oscillator is powered down at hardware reset. It must be enabled (by the NNN register) and
must be allowed to settle for an amount of time specified by USB Oscillator Startup Time parameter in the
device specific manual before using the USB peripheral.
Figure 1-3 shows the overall DSP clock structure. For detailed specifications on clock frequency, voltage
requirements, and oscillator/crystal requirements, see the device-specific data manual.
21
SPRUFX5A–October 2010–Revised November 2010 System Control
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