NuMicro® NUC029LEE/NUC029SEE
32-bit Arm
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Cortex
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-M0 Microcontroller
Aug, 2018
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according to the accurate LXT (32.768 kHz crystal oscillator) or internal USB synchronous mode,
automatically gets accurate HIRC output frequency, 0.25 % deviation within all temperature ranges.
For instance, the system needs an accurate 22.1184 MHz clock. In such case, if users do not want to
use PLL as the system clock source, they need to solder 32.768 kHz crystal in system, and set
FREQSEL (SYS_IRCTCTL[1:
0] trim frequency selection) to “01”, and the auto-trim function will be
enabled. Interrupt status bit FREQ_LOCK (SYS_IRCTSTS[0] HIRC frequency lock status)
“1”
indicates the HIRC output frequency is accurate within 0.25% deviation. To get better results, it is
recommended to set both TRIM_LOOP (SYS_IRCTCTL[5:4]) Trim Calculation Loop and
TRIM_RETRY_CNT (SYS_IRCTCTL[7:6] Trim Value Update Limitation Count
) to “11”.
Another example is that the system needs an accurate 48 MHz clock for USB application. In such
case, if neither using use PLL as the system clock source, user has to set FREQSEL
(SYS_HIRCTCTL1[1:
0] trim frequency selection) to “01”, and the auto-trim function will be enabled.
Status bit FREQLOCK (SYS_HIRCTISTS[8] HIRC Frequency Lock Status)
“1” indicates the HIRC48
output frequency is accurate within 0.25% deviation.