M41ST85WMH6 datasheet(23/41 Pages) STMICROELECTRONICS

23 / 41 page

M41ST85W

Clock operation

23/41

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/FT/OUT pin as shown in Figure 15. To disable 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/FT/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/FT/OUT pin can also be activated in the battery back-up mode. The IRQ/FT/OUT

will go low if an alarm occurs and both ABE (Alarm in Battery Back-up 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 M41ST85W was in the deselect

mode during power-up. Figure 16 on page 24 illustrates the back-up mode alarm timing.

Figure 15.

Alarm interrupt reset waveform

Table 3.

Alarm repeat modes

RPT5

RPT4

RPT3

RPT2

RPT1

Alarm setting

11111

Once per Second

11110

Once per minute

11100

Once per hour

11000

Once per day

10000

Once per month

00000

Once per year

AI03664

IRQ/FT/OUT

ACTIVE FLAG

0Fh

0Eh

10h

HIGH-Z

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