Clock operation

M41T66

18/33

3.3

Setting alarm clock registers

Address locations 0Ah-0Eh 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. Bits RPT5–RPT1 put the alarm in the repeat

mode of operation. Table 3 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.

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/OUT. To disable the alarm, write '0' to the alarm date

register and to RPT5–RPT1.

Note:

If the address pointer is allowed to increment to the flag register address, an alarm condition

will not cause the interrupt/flag to occur until the address pointer is moved to a different

address. It should also be noted that if the last address written is the “alarm seconds,” the

address pointer will increment to the flag address, causing this situation to occur.

The IRQ/OUT output is cleared by a READ to the flags register as shown in Figure 13. A

subsequent READ of the flags register is necessary to see that the value of the alarm flag

has been reset to '0.'

Figure 13.

Alarm interrupt reset waveform

Table 3.

Alarm repeat modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm setting

1

1

1

1

1

Once per second

1

1

1

1

0

Once per minute

1

1

1

0

0

Once per hour

1

1

0

0

0

Once per day

1

0

0

0

0

Once per month

0

0

0

0

0

Once per year