M48T212V datasheet(19/35 Pages) STMICROELECTRONICS

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M48T212V

Clock operation

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3.5

Setting the alarm clock

Address locations 6h-2h contain the alarm settings. 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 programmed to go off while the

M48T212V 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 8 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 condition activates the IRQ/FT pin. To

disable alarm, write '0' to the Alarm Date registers and RPT1-5. The IRQ/FT output is

cleared by a READ to the Flags Register as shown in Figure 7. 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 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 M48T212V was in the deselect mode during

power-up. Figure 8 on page 20 illustrates the back-up mode alarm timing.

Figure 7.

Alarm interrupt reset waveforms

Table 8.

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

AI03021

A0-A3

ACTIVE FLAG BIT

ADDRESS 0h

IRQ/FT

HIGH-Z

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