M41T81S datasheet(15/29 Pages) STMICROELECTRONICS

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M41T81S

Setting Alarm Clock Registers

Address locations 0Ah-0Eh contain the alarm set-

tings. 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 pro-

grammed to go off while the M41T81S is in the

battery back-up mode to serve as a system wake-

up call.

Bits RPT5-RPT1 put the alarm in the repeat mode

of operation. Table 3., page 16 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 (and SQWE is '0.'),

the alarm condition activates the IRQ/FT/OUT/

SQW pin.

Note: If the address pointer is allowed to incre-

ment to the Flags Register address, an alarm con-

dition will not cause the Interrupt/Flag to occur until

the address pointer is moved to a different ad-

dress. It should also be noted that if the last ad-

dress written is the “Alarm Seconds,” the address

pointer will increment to the Flag address, causing

this situation to occur.

The IRQ/FT/OUT/SQW output is cleared by a

READ to the Flags Register as shown in Figure

14. A subsequent READ of the Flags Register is

necessary to see that the value of the Alarm Flag

has been reset to '0.'

The IRQ/FT/OUT/SQW pin can also be activated

in the battery back-up mode. The IRQ/FT/OUT/

SQW will go low if an alarm occurs and both ABE

(Alarm in Battery Back-up Mode Enable) and AFE

are set. Figure 15 illustrates the back-up mode

alarm timing.

Figure 14. Alarm Interrupt Reset Waveform

Figure 15. Back-up Mode Alarm Waveform

IRQ/FT/OUT/SQW

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

AI04617

VCC

IRQ/FT/OUT/SQW

ABE and AFE Bits

AF Bit in Flags

HIGH-Z

VSO

VPFD

trec

AI09164b

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