ST STM8AL, Application Note, Page: 13 / 42

DocID16139 Rev 5 13/42
AN3029 Clock management
41
Figure 6. Crystal/ceramic resonators
1. To avoid exceeding the maximum value of C
L1
and C
L2
(15 pF), it is strongly recommended to use a
resonator with a load capacitance C
L
= 7 pF. To fine-tune the choice, refer to the g
mcrit
calculation in
AN2867 (Oscillator design guide for ST microcontrollers).
2. OSC32_IN and OSC32_OUT pins can be used also as GPIO, but it is recommended not to use them as
both RTC and GPIO pins in the same application.
3. The value of R
EXT
depends on the crystal characteristics. A 0 Ω resistor works with most oscillators. A
typical value is in the range 5 to 6 R
S
. To fine-tune the R
EXT
value refer to AN2867 (Oscillator design guide
for ST microcontrollers).
OSC32_OUT OSC32_IN
ai15764
C
L1
C
L2
Microcontroller
R
EXT
(3)