AT32F425
Series Reference Manual
2022.03.30
Page 423
Ver 2.01
21.6.6 Compare value 2 (ACC_C2)
Bit
Register
Reset value
Type
Description
Bit 31: 16 Reserved
0x0000
resd
Forced to 0 by hardware
Bit 15: 0
C2
0x1F40
rw
Compare 2
This value defines the number of clocks sampled for 8MHz
(ideal frequency) clock in 1ms period , and its default value
is 8000 (theoretical value)
As a center point of cross-return strategy, this value is used
to calculate the calibration value closest to the theoretical
value. In theory, the actual frequency after calibration can
be trimmed to be within an accuracy of 0.5 steps from the
targe frequency (8MHz)
21.6.7 Compare value 3 (ACC_C3)
Bit
Register
Reset value
Type
Description
Bit 31: 16 Reserved
0x0000
resd
Forced to 0 by hardware
Bit 15: 0
C3
0x1F54
rw
Compare 3
This value is the upper boundary for triggering calibration.
When the number of clock sampled by ACC in 1ms period
is greater than or equal to C3, auto calibration is triggered
automatically.
When the actual sampling value (number of clocks in 1ms
period) is greater than C1 but less than C3, auto calibration
is not enabled.