M41ST85WMH6F datasheet(17/34 Pages) STMICROELECTRONICS

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M41ST85W

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 M41ST85W 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 3. shows the possible configu-

rations. 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/FT/OUT pin as shown in

Figure 17.. 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/FT/OUT output is cleared by a READ to

the Flags Register. 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 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 M41ST85W was in the dese-

lect mode during power-up. Figure 18., page 18 il-

lustrates the back-up mode alarm timing.

Figure 17. Alarm Interrupt Reset Waveform

Table 3. 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

AI03664

IRQ/FT/OUT

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

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