ST72325S6B5(2007) View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST72325S6B5
(Rev.:2007)

8-bit MCU with 16 to 60K Flash/ROM, ADC, CSS, 5 timers, SPI, SCI, I2C interface

STMicroelectronics 

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:

■ an external source

■ 4 crystal or ceramic resonator oscillators

■ an internal high frequency RC oscillator

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 Table 6. Refer to the

electrical characteristics section for more details.

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 section 14.1 on page 180 for more details on the

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.

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 6. ST7 Clock Sources

Hardware Configuration

ST7

OSC1

OSC2

EXTERNAL

SOURCE

ST7

OSC1

OSC2

CL1

CL2

LOAD

CAPACITORS

ST7

OSC1

OSC2

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