AT32F413
Series Reference Manual
2022.06.27
Page 329
Rev 2.00
22.4 Functional description
Auto clock calibration (HICK ACC):
implements the sampling and calibration for the HICK clocks by
using the SOF signal (1 ms of period) generated by USB module as a reference signal. In particular, the
HICK clock frequency can be calibrated to a precision of ±0.25% so as to meet the needs of the high-
precision clock applications such as USB.
The signals of the module are connected to the CRM and HICK inside the microcontroller instead of
being connected to the pins externally.
CRM_HICKCAL:
the HICKCAL bit in the CRM module. This signal is used to calibrate the HICK
in bypass mode. The value is defined by the HICKCAL[7: 0] in the CRM_CTRL register.
CRM_HICKTRIM:
the HICKTRIM bit in the CRM module. This signal is used to calibrate the
HICK in bypass mode. The value is defined by the HICKTRIM[5: 0] in the CRM_CTRL register.
The default value of the HICk is 32, which can be calibrated to 8MHz
±
0.25%. The HICK frequency
can be adjusted by 20kHz (design value) each time when the CRM_HICKTRIM value changes.
USB_SOF
: USB Start-of-Frame signal given by the USB device. Its high-level width is 12 system
clock cycles, a pulse signal of 1 ms.
HICKCLK:
HICK clock. The original HICK output frequency is 48MHz, but the sampling clock
used by the HICK calibration module is frequency divider (1/6) clock, about 8MHz.
HICKCAL:
HICK module calibration signal. For the HICK clock after frequency division (1/6), the
HICK clock frequency will change by 40KHz (design value) each time the HICKCAL changes,
which is positively correlated. In other words, the HICK clock frequency will incease by 40KHz
(design value) eac time the HICKCAL is incremented by one; the HICK clock frequency will
reduce by 40KHz each time the HICKCAL is decremented by one.
HICKTRIM:
HICK module calibration signal. For the HICK clock after frequency divion (1/6), the
HICK clock frequency will change by 20KHz (design value) each time the HICKCAL changes,
which is positively correlated.
Refer to
Section 22.6
for more information about the bit definition in the registers.