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The board is equipped with
01
25MHz
crystal oscillator (X5)
circuit that
provides external clock waveform
to the microcontroller OSCO and OSCI
pins. This base frequency is suitable
for further clock multipliers and ideal for
generation of necessary USB clock, which ensures
proper operation of bootloader and your custom USB-
based applications. The board also contains
02
32.768
kHz crystal oscillator (X4)
which provides external clock
for internal RTCC module. Microcontroller ADC requires an accurate
source of reference voltage signal. That is why we provide the external
03
voltage reference
to the microcontroller VREF pin which is
2.048V
.
5. Crystal oscillator and 2.048V reference
01
02
01
02
Figure 5-1: Crystal oscillator
and 2.048V reference
03
03
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