M48T129Y datasheet(17/30 Pages) STMICROELECTRONICS

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M48T129Y, M48T129V

Setting the Alarm Clock

Registers 1FFF6h-1FFF2h 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 month, day,

hour, minute, or second. It can also be pro-

grammed to go off while the M48T129Y/V 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 6., page 17 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.

Note: User must transition address (or toggle Chip

Enable) to see Flag Bit change.

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 pin. To disable alarm,

write ’0’ to the Alarm Date register and RPT1-5.

The IRQ/FT output is cleared by a READ to the

Flags Register as shown in Figure 12. A subse-

quent READ of the Flags Register is necessary to

see that the value of the Alarm Flag has been re-

set to '0.'

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

tery back-up mode. The IRQ/FT 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 M48T129Y/V was in the deselect mode

during power-up. Figure 13., page 18 illustrates

the back-up mode alarm timing.

Figure 12. Alarm Interrupt Reset Waveform

Table 6. Alarm Repeat Mode

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm Activated

Once per Second

Once per Minute

Once per Hour

Once per Day

Once per Month

Once per Year

AI02581

AD0-AD7

ACTIVE FLAG BIT

ADDRESS 1FF0h

IRQ/FT

HIGH-Z

15ns Min

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