M41ST87W_11 datasheet(34/54 Pages) STMICROELECTRONICS

34 / 54 page

Clock operation

M41ST87Y, M41ST87W

34/54

Doc ID 9497 Rev 10

alarm condition activates the IRQ/OUT pin as shown in Figure 25 on page 35. To disable the

alarm, write '0' to the alarm date register and to RPT5–RPT1.

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. Thus the

user should not leave the address pointer at 0Fh if using the alarm interrupt function. This is

easily handled by simply reading past the flags registers before teminating a read sequence.

The IRQ/OUT output is cleared by a READ to the flags register. 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/OUT pin can also be activated in the battery backup mode. The IRQ/OUT 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 M41ST87Y/W was in the deselect mode

during power-up. Figure 25 on page 35 illustrates the backup mode alarm timing.

Figure 24.

Alarm interrupt reset waveform

Table 8.

Alarm repeat modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm setting

1111

Once per second

1110

Once per minute

1100

Once per hour

1000

Once per day

0000

Once per month

0000

Once per year

AI07086

IRQ/OUT

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

ADDRESS POINTER

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