ST10F272B_12 STMICROELECTRONICS [STMicroelectronics], ST10F272B_12 Datasheet - Page 161

• Manufacturer Part Number: ST10F272B_12
• Description: 16-bit MCU with 256 Kbyte Flash memory and 12/20 Kbyte RAM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST10F272B/ST10F272E
24.8.13
Figure 47. 32kHz crystal oscillator connection diagram
Table 75.
The given values of C
printed circuit board: the negative resistance values are calculated assuming additional 5pF
to the values in the table. The crystal shunt capacitance (C
between XTAL3 and XTAL4 pins is globally assumed equal to 4pF. The external resistance
between XTAL3 and XTAL4 is not necessary, since already present on the silicon.
External clock drive XTAL1
When Direct Drive configuration is selected during reset, it is possible to drive the CPU clock
directly from the XTAL1 pin, without particular restrictions on the maximum frequency, since
the on-chip oscillator amplifier is bypassed. The speed limit is imposed by internal logic that
targets a maximum CPU frequency of 64MHz.
In all other clock configurations (Direct Drive with Prescaler or PLL usage) the on-chip
oscillator amplifier is not bypassed, so it determines the input clock speed limit. Then, when
the on-chip oscillator is enabled it is forbidden to use any external clock source different
from crystal or ceramic resonator.
32kHz
Warning:
C
A
Minimum values of negative resistance (module) for 32kHz oscillator
= 6pF
-
Direct driving on XTAL3 pin is not supported. Always use a
32kHz crystal oscillator.
A
C
A
do not include the stray capacitance of the package and of the
= 12pF C
-
Doc ID 11917 Rev 3
A
= 15pF C
-
A
= 18pF C
-
A
0
150 kΩ
) and the package capacitance
= 22pF C
Electrical characteristics
A
120 kΩ
= 27pF C
A
90 kW
= 33pF
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