DocID10772 Rev 7

15/28

M41T00S

Clock operation

Figure 10. Crystal accuracy across temperature

Figure 11. Clock calibration

3.2.1

Century bit

Bits D7 and D6 of clock register 02h contain the CENTURY ENABLE bit (CEB) and the

CENTURY bit (CB). Setting CEB to a '1' will cause CB to toggle, either from a '0' to '1' or

from '1' to '0' at the turn of the century (depending upon its initial state). If CEB is set to a '0,'

CB will not toggle.

3.2.2

Oscillator fail detection

If the Oscillator Fail bit (OF) is internally set to '1,' this indicates that the oscillator has either

stopped, or was stopped for some period of time and can be used to judge the validity of the

clock and date data.

AI07888

–160

0

10

20

30

40

50

60

70

Frequency (ppm)

Temperature

°C

80

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

20

0

–20

= –0.036 ppm/

°C2 ± 0.006 ppm/°C2

K

∆F

= K x (T – T

O)

2

F

T

O = 25°C ± 5°C

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION