M48T36 datasheet(12/17 Pages) STMICROELECTRONICS

12 / 17 page

The IRQ/FT pin is an open drain output which

requires a pull-up resistor for proper operation. A

500-10k

Ω resistor is recommended in order to con-

trol the rise time. The FT bit is cleared on power-up.

SETTING ALARM CLOCK

Registers 7FF5h-7FF2h contain the alarm settings.

The alarm can be configured to go off at a pre-

scribed 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 M48T36 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.

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 condition

activates the IRQ/FT pin. The alarm flag and the

IRQ/FT output are cleared by a read to the Flags

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

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

M48T36 was in the deselect mode during power-

up. Figure 11 illustrates the back-up mode alarm

timing.

RPT4

RPT3

RPT2

RPT1

Alarm Activated

Once per Second

Once per Minute

Once per Hour

Once per Day

Once per Month

Table 11. Alarm Repeat Mode

AI01627

15ns Min

A0-A14

ACTIVE FLAG BIT

IRQ/FT

ADDRESS 1FF0h

HIGH-Z

Figure 10. Interrupt Reset Waveforms

CLOCK OPERATIONS (cont’d)

12/17

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