STFPC320 datasheet(27/78 Pages) STMICROELECTRONICS

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STFPC320

Real-time clock (RTC) operation

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6.6

Setting alarm clock registers

The 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 STFPC320 is in the standby mode to serve as a system wake-up call.

The bits RPT5-RPT1 put the alarm in the repeat mode of operation. Table 5 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_N/SQW pin.

Note:

Note that by default, the alarm repeat mode is enabled and by default the repeat frequency

is set to “once per year”.

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_N/SQW output is cleared by a READ to the flags register as shown in Figure 11. A

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

has been reset to '0’.

Note:

The “Once Per Year” is the default.

Figure 11.

Alarm interrupt reset waveform

Table 5.

Alarm repeat modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm settings

Once per second

Once per minute

Once per hour

Once per day

Once per month

Once per year

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