M41ST87YMX6TR datasheet(28/42 Pages) STMICROELECTRONICS

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M41ST87Y, M41ST87W

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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 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 8., page 28 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 condi-

tion activates the IRQ/OUT pin as shown in Figure

25., page 29. To disable alarm, write '0' to the

Alarm Date Register and to RPT5–RPT1.

Note: If the address pointer is allowed to incre-

ment to the Flag 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/OUT output is cleared by a READ to the

Flags Register. A subsequent READ of the Flags

Alarm Flag has been reset to '0.'

The IRQ/OUT pin can also be activated in the bat-

tery back-up mode. The IRQ/OUT will go low if an

alarm occurs and both ABE (Alarm in Battery

Back-up Mode Enable) and AFE are set. The ABE

and AFE Bits are reset during power-up, therefore

an alarm generated during power-up will only set

AF. The user can read the Flag Register at system

boot-up to determine if an alarm was generated

while the M41ST87Y/W was in the deselect mode

during power-up. Figure 25., page 29 illustrates

the back-up mode alarm timing.

Figure 24. Alarm Interrupt Reset Waveform

Table 8. Alarm Repeat Modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm Setting

1111

Once per Second

1110

Once per Minute

1100

Once per Hour

1000

Once per Day

0000

Once per Month

0000

Once per Year

AI07086

IRQ/OUT

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

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