CMOSTEK CMT2380F17, Manual

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CMT2380F17
Rev0.1 | 69/347
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frequency is 50MHz. Please note, when using Clock Multiplier (CKM) to raise the MCK frequency to get
higher SYSCLK, the CPUCLK will be also changed. It is need to set CCKS to slow down CPUCLK before
raise MCK frequency to avoid CPUCLK over clock (CPUCLK needs to lower then 25MHz or 36MHz).
The clock module also provide two more clock source for high speed PCA applications.
-
MCKDO: Up to 72MHz
-
CKMIX16: Up to 144MHz
Figure 9-1. System Clock
9.2 Clock Source Switching
There are three clock sources for the system clock: Internal High-frequency RC Oscillator (IHRCO),
Internal Low-frequency RC Oscillator (ILRCO) and External Clock Input. Figure 9
–1 shows the structure of the
system clock in CMT2380F17. The CMT2380F17 always boots from IHRCO on 12MHz. OSCS[1:0] are used
to select the clock source by software setting, but the software need to wait until the clock be settle before
switch the clock source.
。
9.3 On-chip CKM (PLL)
There are three clock sources for the system clock: Internal High-frequency RC Oscillator (IHRCO),
Internal Low-frequency RC Oscillator (ILRCO) and External Clock Input. Figure 9
–1 shows the structure of the
system clock in CMT2380F17. The CMT2380F17 always boots from IHRCO on 12MHz. OSCS[1:0] are used
to select the clock source by software setting, but the software need to wait until the clock be settle before
switch the clock source.
。
9.4 Wake-up clock from CKM
When enable CKM circuit, it needs 100us to output stable frequency, within this uncertain frequency
period, the input of the MCK needs to keep MCKS on OSCin to guarantee system’s satiability. Please
reference the following procedure:
How to Program to Support wake-up with clock from CKM

Program MCKS[1:0] (CKCON
2.3~2) to “00” to select non-CKM output as clock source

MCU enters power down

……………
..

MCU wakes up

delay 100us to wait CKM working stable.

Modify MCKS[1:0] (CKCON2.3~2) to select CKM output as clock source