Clock operations

M48T37Y, M48T37V

14/30

Doc ID 7019 Rev 9

3.4

Setting the alarm clock

Registers 7FF5h-7FF2h contain the alarm settings. The alarm can be configured to go off at

a predetermined 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 M48T37Y/V is in the battery backup

mode of operation to serve as a system wake-up call.

RPT1-RPT4 put the alarm in the repeat mode of operation. Table 6 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 RPT1-RPT4, AF is set. If AFE is also set, the alarm condition 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 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 backup mode. The IRQ/FT will go low if

an alarm occurs and both the alarm in battery backup mode enable (ABE) and the 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 M48T37Y/V was in the deselect mode during

power-up. Figure 8 illustrates the backup mode alarm timing.

Figure 7.

Alarm interrupt reset waveform

Table 6.

Alarm repeat modes

RPT4

RPT3

RPT2

RPT1

Alarm activated

1

1

1

1

Once per second

1

1

1

0

Once per minute

1

1

0

0

Once per hour

1

0

0

0

Once per day

0

0

0

0

Once per month

AI01677B

A0-A14

ACTIVE FLAG BIT

ADDRESS 7FF0h

IRQ/FT

15ns Min