M263 datasheet(297/398 Pages) NUVOTON

297 / 398 page

M261/M262/M263

Mar 25, 2020

Page 297 of 398

Rev 1.02

System and peripheral can use the clock as its operating clock only when correlate clock stable index

is set to 1. The clock stable index will be auto cleared when the clock source (HXTEN

(CLK_PWRCTL[0]),

LXTEN

(CLK_PWRCTL[1]),

LIRC32KEN

(RTC_LXTCTL[0]),

HIRCEN

(CLK_PWRCTL[2]),

LIRCEN

(CLK_PWRCTL[3]),

HIRC48EN

(CLK_PWRCTL[18])

and

(CLK_PLLCTL[16])) are disabled.

Besides, the clock stable index of HXT, HIRC, HIRC48 and PLL will be auto cleared when chip enters

power-down and clock stable counter will re-count after chip wake-up if correlate clock is enabled.

6.3.3

System Clock and SysTick Clock

The system clock has 6 clock sources which are generated from clock generator block. The clock

source switch depends on the register HCLKSEL (CLK_CLKSEL0[2:0]). The block diagram is shown

in Figure 6.3-5.

011

010

001

PLLFOUT

LXT

HXT

LIRC

HCLKSEL

(CLK_CLKSEL0[2:0])

HIRC

000

HCLKDIV

(CLK_CLKDIV0[3:0])

CPU in Power Down Mode

CPU

AHB

APB1

CPUCLK

HCLK

PCLK1

111

1/(HCLKDIV+1)

APB0

PCLK0

100

HIRC48

Note:

Before clock switching, both the pre-selected and newly selected clock sources must be turned on and stable.

Figure 6.3-5 System Clock Block Diagram

There are two clock fail detectors to observe HXT and LXT clock source and they have individual

enable and interrupt control. When HXT detector is enabled, the HIRC clock is enabled automatically.

When LXT detector is enabled, the LIRC clock is enabled automatically.

When HXT clock detector is enabled, the system clock will auto switch to HIRC if HXT clock stop

being detected on the following condition: system clock source comes from HXT or system clock

source comes from PLL with HXT as the input of PLL. If HXT clock stop condition is detected, the

HXTFIF (CLK_CLKDSTS[0]) is set to 1 and chip will enter interrupt if HXTFIE (CLK_CLKDCTL[5]) is

set to 1. HXT clock source stable flag, HXTSTB (CLK_STATUS[0]), will be cleared if HXT stops when

using HXT fail detector function. User can try to recover HXT by disable HXT and enable HXT again to

check if the clock stable bit is set to 1 or not. If HXT clock stable bit is set to 1, it means HXT is recover

to oscillate after re-enable action and user can switch system clock to HXT again.

The HXT clock stop detect and system clock switch to HIRC procedure is shown in Figure 6.3-6.

M263 Datasheet(PDF) 297 Page - Nuvoton Technology Corporation

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