![](http://datasheet.mmic.net.cn/100000/IF180C52TXXX-20R_datasheet_3493957/IF180C52TXXX-20R_192.png)
192
32099I–01/2012
AT32UC3L016/32/64
Figure 13-3. DFLL Locking in Closed loop
CLK_DFLL is ready to be used when the DFLLn Synchronization Ready bit (DFLLnRDY) in
PCLKSR is set after enabling the DFLL. However, the accuracy of the output frequency depends
on which locks are set.
For lock times, please refer to the Electrical Characteristics chapter.
Drift compensation
The frequency tuner will automatically compensate for drift in the f
DFLL without losing either of the
locks. If the FINE value overflows or underflows, which should normally not happen, but could
occur due to large drift in temperature and voltage, all locks will be lost, and the COARSE and
FINE values will be recalibrated as described earlier. If any lock is lost the corresponding bit in
PCLKSR will be set, DFLLn Lock Lost on Coarse Value bit (DFLLnLOCKLOSTC) for lock lost on
COARSE value, DFLLn Lock Lost on Fine Value bit (DFLLnLOCKLOSTF) for lock lost on FINE
value and DFLLn Lock Lost on Accurate Value bit (DFLLnLOCKLOSTA) for lock lost on ACCU-
RATE value. The corresponding lock status bit will be cleared when the lock lost bit is set, and
vice versa.
Reference clock stop detection
If CLK_DFLLIF_REF stops or is running at a very slow frequency, the DFLLn Reference Clock
Stopped bit (DFLLnRCS) in PCLKSR will be set. Note that the detection of the clock stop will
take a long time. The DFLLIF operate as if it was in open loop mode if it detects that the refer-
ence clock has stopped. This means that the COARSE and FINE values will be kept constant
while PCLKSR.DFLLnRCS is set. Closed loop mode operation will automatically resume if the
CLK_DFLLIF_REF is restarted, and compensate for any drift during the time CLK_DFLLIF_REF
was stopped. No locks will be lost.
Frequency error measurement
The ratio between CLK_DFLLIF_REF and CLK_DFLL is measured automatically by the DFLLIF.
The difference between this ratio and DFLLnMUL is stored in the Multiplication Ratio Difference
field (RATIODIFF) in the DFLLn Ratio Register (DFLLnRATIO). The relative error on CLK_DFLL
compared to the target frequency can be calculated as follows:
Initial
frequency
Target
frequency
DFLLnLOCKC DFLLnLOCKF DFLLnLOCKA