M41ST87WMX6TR datasheet(32/54 Pages) STMICROELECTRONICS

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Clock operation

M41ST87W

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DocID9497 Rev 11

Figure 22: Crystal accuracy across temperature

Figure 23: Calibration waveform

3.4

Setting alarm clock registers

Address locations 0Ah-0Eh contain the alarm settings. The alarm can be configured to go

off at a prescribed time on a specific month, date, hour, minute, or second, or repeat every

year, month, day, hour, minute, or second. It can also be programmed to go off while the

M41ST87Y/W is in the battery back-up to serve as a system wake-up call.

Bits RPT5–RPT1 put the alarm in the repeat mode of operation. Table 9: "Alarm repeat

modes" shows the possible configurations. Codes not listed in the table default to the once

per second mode to quickly alert the user of an incorrect alarm setting.

When the clock information matches the alarm clock settings based on the match criteria

defined by RPT5–RPT1, the AF (alarm flag) is set. If AFE (alarm flag enable) is also set,

the alarm condition activates the

IRQ/OUTpinasshowninFigure25:"Backupmodealarm

waveform". To disable the alarm, write '0' to the alarm date register and to RPT5–RPT1.

If the address pointer is allowed to increment to the flag register address, an alarm

condition will not cause the interrupt/flag to occur until the address pointer is moved to a

different address. It should also be noted that if the last address written is the “alarm

seconds,” the address pointer will increment to the flag address, causing this situation to

occur. Thus the user should not leave the address pointer at 0Fh if using the alarm

–160

Frequency (ppm)

Temperature

°C

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

–20

= –0.036 ppm/

°C 2 ± 0.006 ppm/ °C 2

= K x (T – T

O )

O = 25 °C ± 5 °C

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION

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