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Auto-wakeup (AWU)

RM0016

 

 

12.3.2Time base selection

Please refer to the Asynchronous prescaler register (AWU_APR) and Timebase selection register (AWU_TBR) descriptions.

The AWU time intervals depend on the values of:

AWUTB[3:0] bits. This gives the counter output rank.

APR[5:0] bits. This gives the prescaler division factor (APRDIV).

15 non-overlapped ranges of time intervals can be defined as follows:

Table 25. Time base calculation table

Interval range

 

APRDIV formula for

APRDIV

 

 

AWUTB[3:0]

time interval

fLS = f

fLS = 128kHz

 

calculation

range

 

 

 

 

 

 

 

 

 

2/f - 64/f

0.015625 ms - 0.5 ms

0001

APRDIV/fLS

 

 

2 to 64

2x32/f - 2x2x32/f

0.5 ms - 1.0 ms

0010

2 x APRDIV/fLS

32 to 64

2x64/f - 2x2x64/f

1 ms - 2 ms

0011

22 x APR

/f

LS

32 to 64

 

 

 

DIV

 

 

22x64/f - 22x128/f

2 ms - 4ms

0100

23 x APRDIV/fLS

32 to 64

23x64/f - 23x128/f

4 ms - 8 ms

0101

24 x APRDIV/fLS

32 to 64

24x64/f - 24x128/f

8 ms - 16 ms

0110

25 x APRDIV/fLS

32 to 64

25x64/f - 25x128/f

16 ms - 32 ms

0111

26 x APRDIV/fLS

32 to 64

26x64/f - 26x128/f

32 ms - 64 ms

1000

27 x APRDIV/fLS

32 to 64

27x64/f - 27x128/f

64 ms - 128 ms

1001

28 x APRDIV/fLS

32 to 64

28x64/f - 28x128/f

128 ms - 256 ms

1010

29 x APRDIV/fLS

32 to 64

29x64/f - 29x128/f

256 ms - 512 ms

1011

210 x APRDIV/fLS

32 to 64

210x64/f - 210x128/f

512 ms - 1.024 s

1100

211 x APRDIV/fLS

32 to 64

211x64/f - 211x128/f

1.024 s - 2.048 s

1101

212 x APRDIV/fLS

32 to 64

211x130/f - 211x320/f

2.080 s - 5.120 s

1110

5 x 211 x APRDIV/fLS

26 to 64

211x330/f - 212x960/f

5.280 s - 30.720s

1111

30 x 211 x APRDIV/fLS

11 to 64

In order to obtain the right values for AWUTB[3:0] and APRDIV, you have to:

First, search the interval range corresponding to the desired time interval. This gives the AWUTB[3:0] value.

Then APRDIV can be chosen to obtain a time interval value as close as possible to the desired one. This can be done using the formulas listed in the table above.

Note:

If the target value is between 211x128/fLS and 211x130/fLS or between 211x320/fLS and

 

211x330/f , the value closer to the target one must be chosen.

 

LS

116/454

Doc ID 14587 Rev 9

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