RM0312 datasheet(86/275 Pages) STMICROELECTRONICS

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Auto-wakeup (AWU)

RM0312

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DocID022352 Rev 3

12.3.2

Time base selection

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

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:

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/fLS, the value closer to the target one must be chosen.

Table 23. Time base calculation table

Interval range

AWUTB[3:0]

APRDIV formula for

time interval

calculation

APRDIV

range

fLS = f

fLS = 38 kHz

2/f - 64/f

0.53 ms - 1.68 ms

0001

APRDIV/fLS

2 to 64

2x32/f - 2x2x32/f

1.68 ms - 3.37 ms

0010

2 x APRDIV/fLS

32 to 64

2x64/f - 2x2x64/f

3.37 ms - 6.74 ms

0011

22 x APRDIV/fLS

32 to 64

22x64/f - 22x128/f

6.74 ms - 13.47 ms

0100

23 x APRDIV/fLS

32 to 64

23x64/f - 23x128/f

13.47 ms - 26.95 ms

0101

24 x APRDIV/fLS

32 to 64

24x64/f - 24x128/f

26.95 ms - 53.89 ms

0110

25 x APRDIV/fLS

32 to 64

25x64/f - 25x128/f

53.89 ms - 107.8 ms

0111

26 x APRDIV/fLS

32 to 64

26x64/f - 26x128/f

107.8 ms - 215.6 ms

1000

27 x APRDIV/fLS

32 to 64

27x64/f - 27x128/f

215.6 ms - 431.2 ms

1001

28 x APRDIV/fLS

32 to 64

28x64/f - 28x128/f

431.2 ms - 862.3 ms

1010

29 x APRDIV/fLS

32 to 64

29x64/f - 29x128/f

862.3 ms - 1.72 s

1011

210 x APRDIV/fLS

32 to 64

210x64/f - 210x128/f

1.72 s - 3.45 s

1100

211 x APRDIV/fLS

32 to 64

211x64/f - 211x128/f

3.45 s - 6.90 s

1101

212 x APRDIV/fLS

32 to 64

211x130/f - 211x320/f

7.01 s - 17.25 s

1110

5 x 211 x APRDIV/fLS

26 to 64

211x330/f - 212x960/f

17.79 s - 103.48 s

1111

30 x 211 x APRDIV/fLS

11 to 64

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