ST72C334J4TAE STMicroelectronics, ST72C334J4TAE Datasheet - Page 30

• Manufacturer Part Number: ST72C334J4TAE
• Description: 8-bit MCU for automotive with single voltage Flash/ROM memory, ADC, 16-bit timers, SPI, SCI interfaces
• Manufacturer: STMicroelectronics

ST72334xx-Auto, ST72314xx-Auto, ST72124Jx-Auto
8.3 MULTI-OSCILLATOR (MO)
The main clock of the ST7 can be generated by
four 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
configuration are shown in
ELECTRICAL CHARACTERISTICS
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 four oscilla-
tors with different frequency ranges has to be done
by option byte in order to reduce consumption. In
this mode of the multi-oscillator, 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 capacitance values must be adjusted
according to the selected oscillator.
These oscillators are not stopped during the RE-
SET phase to avoid losing time in the oscillator
start-up phase.
External RC Oscillator
This oscillator allows a low cost solution for the
main clock of the ST7 using only an external resis-
tor and an external capacitor. The frequency of the
external RC oscillator (in the range of some MHz)
is fixed by the resistor and the capacitor values.
Consequently in this MO mode, the accuracy of
the clock is dependent on V
tions and the accuracy of the discrete components
used. This option should not be used in applica-
tions that require accurate timing.
Internal RC Oscillator
The internal RC oscillator mode is based on the
same principle as the external RC oscillator includ-
ing the resistance and the capacitance of the de-
vice. This mode is the most cost effective one with
30/150
an external source
4 crystal or ceramic resonator oscillators
an external RC oscillator
an internal high frequency RC oscillator
DD
Table
, T
A
, process varia-
4. Refer to the
section for
the drawback of a lower frequency accuracy. Its
frequency is in the range of several MHz. This op-
tion should not be used in applications that require
accurate timing.
In this mode, the two oscillator pins have to be tied
to ground.
Table 4. ST7 Clock Sources
R
C
L1
EX
EXTERNAL
Hardware Configuration
SOURCE
OSC1
OSC1
OSC1
OSC1
CAPACITORS
LOAD
ST7
ST7
ST7
ST7
OSC2
OSC2
OSC2
OSC2
C
C
EX
L2