M41T81

Clock operation

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3.4

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. It can also be programmed to go off while the

M41T81 is in the battery back-up mode to serve as a system wake-up call.

Bits RPT5-RPT1 put the alarm in the repeat mode of operation. Table 3 on page 18 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

(and SQWE is '0.'), the alarm condition activates the IRQ/FT/OUT/SQW pin.

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/FT/OUT/SQW output is cleared by a READ to the Flags Register as shown in

Figure 12. 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/OUT/SQW pin can also be activated in the battery back-up mode. The

IRQ/FT/OUT/SQW will go low if an alarm occurs and both ABE (Alarm in Battery Back-up

Mode Enable) and AFE are set. Figure 13 illustrates the back-up mode alarm timing.

Figure 12.

Alarm interrupt reset waveform

IRQ/FT/OUT/SQW

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

AI04617