st10f272z2 STMicroelectronics, st10f272z2 Datasheet - Page 164

• Manufacturer Part Number: st10f272z2
• Description: 16-bit Mcu With 256 Kbyte Flash Memory And 20 Kbyte Ram
• Manufacturer: STMicroelectronics

Electrical characteristics
25.8.13
164/189
Table 76.
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 64 MHz.
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.
Table 77.
1. The minimum value for the XTAL1 signal period shall be considered as the theoretical minimum. The real
2. 4-8 MHz is the input frequency range when using an external clock source. 64 MHz can be applied with an
3. The input clock signal must reach the defined levels V
XTAL1 period
High time
Low time
Rise time
Fall time
32kHz
minimum value depends on the duty cycle of the input clock signal.
external clock source only when Direct Drive mode is selected: in this case, the oscillator amplifier is
bypassed so it does not limit the input frequency.
Parameter
Warning:
3
3
3
3
C
A
Minimum values of negative resistance (module) for 32 kHz oscillator
External clock drive
1, 2
= 6 pF C
-
t
t
t
t
t
OSC
1
2
3
4
Direct driving on XTAL3 pin is not supported. Always use a
32 kHz crystal oscillator.
Symbol
A
SR
SR
SR
SR
SR
A
do not include the stray capacitance of the package and of the
= 12 pF C
-
15.625
min.
Direct drive
f
6
6
–
–
CPU
A
= 15 pF C
= f
-
XTAL
max.
–
–
–
2
2
IL2
A
= 18 pF C
and V
Direct drive with
-
f
min.
83.3
CPU
3
3
–
–
prescaler
IH2
= f
.
XTAL
A
0
150 kΩ
) and the package capacitance
max.
= 22 pF C
250
–
–
2
2
/ 2
f
CPU
min.
83.3
A
120 kΩ
6
6
–
–
PLL usage
= 27 pF C
= f
XTAL
ST10F272Z2
max.
250
–
–
2
2
x F
A
90 kW
= 33 pF
Unit
ns
ns
ns
ns
ns