M48T559Y datasheet(11/18 Pages) STMICROELECTRONICS

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M48T559Y

For more information on calibration, see the Appli-

cation Note AN934 "TIMEKEEPER Calibration".

The IRQ/FT pin is an open drain output which re-

quires a pull-up resistor for proper operation. A

500-10k

Ω resistor is recommended in order to

control the rise time.

SETTING ALARM CLOCK

Registers 1FF5h-1FF2h contain the alarm set-

tings. The alarm can be configured to go off at a

prescribed time on a specific day of the month or

repeat every day, hour, minute, or second. It can

also be programmed to go off while the M48T559Y

is in the battery back-up mode of operation to

serve as a system wake-up call.

RPT1-RPT4 put the alarm in the repeat mode of

operation. Table 11 shows the possible configura-

tions. 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 RPT1-RPT4, 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 registers and RPT1-4.

The alarm flag and the IRQ/FT output are cleared

by a read to the Flags register as shown in Figure

11.

Note: If an alarm condition occurs while the flags

the alarm flag will not be set until an address other

than the flags register (1FF0h) is latched into the

address buffer. This will insure that the alarm flag

will not be inadvertently reset while reading the

flag register. To properly check to see if an alarm

condition has occurred while reading the flag reg-

ister, the user is required to latch, read or write to

an alternate address and then re-read the alarm

flag.

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 M48T559Y was in the deselect mode

during power-up. Figure 12 illustrates the back-up

mode alarm timing.

Figure 10. Interrupt Reset Waveforms

AI01677B

AD0-AD7

ACTIVE FLAG BIT

ADDRESS 1FF0h

IRQ/FT

Table 11. Alarm Repeat Mode

RPT4

RPT3

RPT2

RPT1

Alarm Activated

Once per Second

Once per Minute

Once per Hour

Once per Day

Once per Month

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