M41T94 datasheet(18/31 Pages) STMICROELECTRONICS

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M41T94

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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 M41T94 is in the bat-

tery back-up to serve as a system wake-up call.

Bits RPT5-RPT1 put the alarm in the repeat mode

of operation. Table 11, page 18 shows the possi-

ble configurations. Codes not listed in the table de-

fault 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/FT/OUT pin.

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.

To disable the alarm, write '0' to the Alarm Date

is cleared by a READ to the Flags Register. This

READ of the Flags Register will also reset the

Alarm Flag (D6; Register 0Fh). See Figure 15,

page 18.

The IRQ/FT/OUT pin can also be activated in the

battery back-up mode. The IRQ/FT/OUT will go

low if an alarm occurs and both ABE (Alarm in Bat-

tery 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 M41T94 was in the deselect

mode during power-up. Figure 16, page 19 illus-

trates the back-up mode alarm timing.

Table 11. Alarm Repeat Mode

Figure 15. Alarm Interrupt Reset Waveforms

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

AI03664

IRQ/FT/OUT

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

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