• External oscillator (XOSC) module — The external oscillator providing reference
clock to internal clock source (ICS), the real-time clock counter clock module (RTC)
and other MCU sub-systems.
• Low-power oscillator (LPO) module — The on-chip low-power oscillator providing
1 kHz reference clock to RTC and watchdog (WDOG).
NOTE
For this device, the system clock is the bus clock.
The following figure shows a simplified clock connection diagram.
ICSLCLK
ICSFFCLK
XTAL
EXTAL
WDG
RTC
FTM0
FTM1
ADC
SCI0
CPU
BDC
FLASH
ACMP
RAM
LPOCLK
ICS
OSC
OSCOUT
1-kHz
LPO
ICSIRCLK
IPC
DBG
KBI0
TCLK1
TCLK0
ICSCLK (~8 MHz after reset)
1/2
FTM2
Figure 1-2. System clock distribution diagram
The clock system supplies:
• ICSCLK(BUS) — This up to 20 MHz clock source is used as the bus clock that is
the reference to CPU and all peripherals. Control bits in the ICS control registers
determine which of the clock sources is connected:
• Internal reference clock
• External reference clock
• Frequency-locked loop (FLL) output
• ICSLCLK — This clock source is derived from the digitally controlled oscillator
(DCO) of the ICS when the ICS is configured to run off of the internal or external
reference clock. Development tools can select this internal self-clocked source (8
MHz) to speed up BDC communications in systems where the bus clock is slow.
System clock distribution
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