ST92F120JR9T datasheet(104/320 Pages) STMICROELECTRONICS

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ST92F120 - RESET AND CLOCK CONTROL UNIT (RCCU)

Figure 48. Example of Low Power mode programming in WFI using CK_AF external clock

User’s Program

WFI instruction

PROGRAM FLOW

INTCLK FREQUENCY

Interrupt

PLL multiply factor

Divider factor set

Wait for the PLL to lock

CK_AF clock selected

Wait For Interrupt

No code is executed until

Interrupt serviced

set to 10

to 1, and PLL turned ON

an interrupt is requested

Low Power Mode enabled

2 MHz

20 MHz

2MHz

20 MHz

** TSTUP = Quartz oscillator start-up time

*TPLK = PLL lock-in time

TPLK*

FXtal = 4 MHz, VDD = 4.5 V min

WAIT

CSU_CKSEL

← 1PLL is system clock source

while CK_AF is

the System Clock

and the Xtal restarts

FCK_AF

The System Clock

switches to Xtal

in WFI state

User’s Program

Preselect Xtal stopped

when CK_AF selected

activated

Wait for the Xtal

WAIT

PLL is System Clock source

to stabilise

Wait for the PLL to lock

WAIT

WFI_CKSEL

← 1

XTSTOP

← 1

LPOWF I

← 1

WFI status

Interrupt Routine

XTSTOP

← 0

CKAF_SEL

← 0

CSU_CKSEL

← 1

DX2-0

← 000

MX(1:0)

← 00

Reset State

CK_AF selected and Xtal stopped

automatically

Begin

Execution of user program

resumes at full speed

TSTUP**

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