Clock operations

M48T129V, M48T129Y

16/28

Doc ID 5710 Rev 4

3.6

Setting the alarm clock

Registers 1FFF6h-1FFF2h 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

month, day, hour, minute, or second. It can also be programmed 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 on page 16 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

register and RPT1-5. The IRQ/FT output is cleared by a READ to the flags register as

shown in Figure 10 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 backup 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 11 on page 17 illustrates the backup mode alarm timing.

Figure 10.

Alarm interrupt reset waveform

Table 6.

Alarm repeat mode

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm activated

1

1

1

1

1

Once per second

11

110

Once per minute

1

1

1

0

0

Once per hour

11

000

Once per day

10

000

Once per month

00

000

Once per year

AI02581

AD0-AD7

ACTIVE FLAG BIT

ADDRESS 1FF0h

IRQ/FT

HIGH-Z

15ns Min