ST72321AR7 STMicroelectronics, ST72321AR7 Datasheet - Page 25

• Manufacturer Part Number: ST72321AR7
• Description: 8-BIT MCU WITH NESTED INTERRUPTS, FLASH,10-BIT ADC, FIVE TIMERS, SPI, SCI, I2C INTERFACE
• Manufacturer: STMicroelectronics

Specifications of ST72321AR7

• Hdflash Endurance: 100 cycles, data retention
• Clock Sources: crystal/ceramic resonator oscillators, internal RC oscillator, clock security system and bypass for external clock
• Four Power Saving Modes: Halt, Active-Halt,Wait and Slow
• Main Clock Controller With: Real time base, Beep and Clock-out capabilities
• Two 16-bit Timers With: 2 input captures, 2 output compares, external clock input on one timer, PWM and pulse generator modes
• 8-bit Pwm Auto-reload Timer With: 2 input captures, 4 PWM outputs, output compare and time base interrupt, external clock with event detector

6.2 MULTI-OSCILLATOR (MO)
The main clock of the ST7 can be generated by
three different source types coming from the multi-
oscillator block:
■
■
■
Each oscillator is optimized for a given frequency
range in terms of consumption and is selectable
through the option byte. The associated hardware
configurations are shown in
electrical characteristics section for more details.
Caution: The OSC1 and/or OSC2 pins must not
be left unconnected. For the purposes of Failure
Mode and Effect Analysis, it should be noted that if
the OSC1 and/or OSC2 pins are left unconnected,
the ST7 main oscillator may start and, in this con-
figuration, could generate an f
in excess of the allowed maximum (>16MHz.),
putting the ST7 in an unsafe/undefined state. The
product behaviour must therefore be considered
undefined when the OSC pins are left unconnect-
ed.
External Clock Source
In this external clock mode, a clock signal (square,
sinus or triangle) with ~50% duty cycle has to drive
the OSC1 pin while the OSC2 pin is tied to ground.
Crystal/Ceramic Oscillators
This family of oscillators has the advantage of pro-
ducing a very accurate rate on the main clock of
the ST7. The selection within a list of 4 oscillators
with different frequency ranges has to be done by
option byte in order to reduce consumption (refer
to
frequency ranges). In this mode of the multi-oscil-
lator, the resonator and the load capacitors have
to be placed as close as possible to the oscillator
pins in order to minimize output distortion and
start-up stabilization time. The loading capaci-
tance values must be adjusted according to the
selected oscillator.
These oscillators are not stopped during the
RESET phase to avoid losing time in the oscillator
start-up phase.
section 14.1 on page 175
an external source
4 crystal or ceramic resonator oscillators
an internal high frequency RC oscillator
for more details on the
Table
OSC
clock frequency
5. Refer to the
Internal RC Oscillator
This oscillator allows a low cost solution for the
main clock of the ST7 using only an internal resis-
tor and capacitor. Internal RC oscillator mode has
the drawback of a lower frequency accuracy and
should not be used in applications that require ac-
curate timing.
In this mode, the two oscillator pins have to be tied
to ground.
Table 5. ST7 Clock Sources
ST72321Rx ST72321ARx ST72321Jx
C
L1
Hardware Configuration
EXTERNAL
SOURCE
OSC1
OSC1
OSC1
CAPACITORS
LOAD
ST7
ST7
ST7
OSC2
OSC2
OSC2
C
L2
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