Datasheet

ST72321Rx ST72321ARx ST72321Jx
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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 11.
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
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 f
OSC2
of 4 to 8
MHz. The PLL is enabled by option byte. If the PLL
is disabled, then f
OSC2 =
f
OSC
/2.
Caution: The PLL is not recommended for appli-
cations where timing accuracy is required. See
“PLL Characteristics” on page 151.
Figure 10. PLL Block Diagram
Figure 11. Clock, Reset and Supply Block Diagram
0
1
PLL OPTION BIT
PLL x 2
f
OSC2
/ 2
f
OSC
LOW VOLTAGE
DETECTOR
(LVD)
f
OSC2
AUXILIARY VOLTAGE
DETECTOR
(AVD)
MULTI-
OSCILLATOR
(MO)
OSC1
RESET
V
SS
EVD
V
DD
RESET SEQUENCE
MANAGER
(RSM)
OSC2
MAIN CLOCK
AVD Interrupt Request
CONTROLLER
PLL
SYSTEM INTEGRITY MANAGEMENT
WATCHDOG
SICSR
TIMER (WDG)
WITH REALTIME
CLOCK (MCC/RTC)
AVD
AVD AVD
LVD
RF
IE
WDG
RF
0
1
f
OSC
(option)
0
S
F
f
CPU
00