AT32F425
Series Reference Manual
2022.03.30
Page 418
Ver 2.01
21
HICK auto clock calibration (ACC)
21.1
ACC introduction
HICK auto clock calibration (HICK ACC), which uses the SOF signal (1 ms of period) generated as a
reference signal, implements the sampling and calibration for the HICK clocks.
The main pupose of this module is to provide a clock of 48MHz±0.25% for the USB device.
It is able to make the calibrated frequency as close to the target frequency as possible by means of
“cross and return” algorithm.
21.2
Main features
Programmable center frequency
Programmable boundary frequency that triggers calibration function
Center frequency precision ±0.25%
Status detection flags
―
Calibration ready flag
Error detection flags
―
Reference signal lost error flag
Two interrupt source flag
―
Calibration ready flag
―
Reference signal lost error flag
Two calibration modes: coarse calibration and fine calibration
21.3
Interrupt requests
Table 21-1 ACC interrupt requests
Interrupt event
Event flag
Enable bit
Calibration ready
CALRDY
CALRDYIEN
Reference signal lost
RSLOST
EIEN
ACC interrupt events are linked to the same interrupt vector (see
). Interrupt events include:
During calibration process: When the calibration gets ready or reference signal lost occurs,
the corresponding interrupt will be generated if the corresponding enable bit is enabled.
Figure 21-1 ACC interrupt mapping diagram
ACC interrupt
CALRDY
CALRDYIEN
RSLOST
EIEN
21.4
Functional description
Auto clock calibration (HICK ACC), which uses the SOF signal (1 ms of period) generated as a reference
signal, implements the sampling and calibration for the HICK clocks. 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.