ST72521 datasheet(24/211 Pages) STMICROELECTRONICS

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ST72521

24/211

6 SUPPLY, RESET AND CLOCK MANAGEMENT

The device includes a range of utility features for

securing the application in critical situations (for

example in case of a power brown-out), and re-

ducing the number of external components. An

overview is shown in Figure 10.

For more details, refer to dedicated parametric

section.

Main features

Optional PLL for multiplying the frequency by 2

(not to be used with internal RC oscillator)

Reset Sequence Manager (RSM)

Multi-Oscillator Clock Management (MO)

– 5 Crystal/Ceramic resonator oscillators

– 1 Internal RC oscillator

System Integrity Management (SI)

– Main supply Low voltage detection (LVD)

– Auxiliary Voltage detector (AVD) with interrupt

capability for monitoring the main supply or

the EVD pin

– Clock Security System (CSS) with Clock Filter

and Backup Safe Oscillator (enabled by op-

tion byte)

6.1 PHASE LOCKED LOOP

If the clock frequency input to the PLL is in the

range 2 to 4 MHz, the PLL can be used to multiply

the frequency by two to obtain an fOSC2 of 4 to 8

MHz. The PLL is enabled by option byte. If the PLL

is disabled, then fOSC2 = fOSC/2.

Caution: The PLL is not recommended for appli-

cations where timing accuracy is required. See

“PLL Characteristics” on page 176.

Figure 9. PLL Block Diagram

Figure 10. Clock, Reset and Supply Block Diagram

PLL OPTION BIT

PLL x 2

fOSC2

/ 2

fOSC

LOW VOLTAGE

DETECTOR

(LVD)

fOSC2

AUXILIARY VOLTAGE

DETECTOR

(AVD)

MULTI-

OSCILLATOR

(MO)

OSC1

RESET

VSS

EVD

VDD

RESET SEQUENCE

MANAGER

(RSM)

CLOCK

FILTER

SAFE

OSC

CLOCK SECURITY SYSTEM

(CSS)

OSC2

MAIN CLOCK

CSS Interrupt Request

AVD Interrupt Request

CONTROLLER

PLL

SYSTEM INTEGRITY MANAGEMENT

WATCHDOG

SICSR

TIMER (WDG)

WITH REALTIME

CLOCK (MCC/RTC)

AVD AVD AVD LVD

CSS

WDG

fOSC

fOSC2

(option)

fCPU

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