m41st84w STMicroelectronics, m41st84w Datasheet - Page 17

• Manufacturer Part Number: m41st84w
• Description: 3.0/3.3v I 2c Serial Rtc With Supervisory Functions
• Manufacturer: STMicroelectronics

Setting Alarm Clock Registers
Address locations 0Ah-0Eh contain the alarm set-
tings. 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 pro-
grammed to go off while the M41ST84W is in the
battery back-up to serve as a system wake-up call.
Bits RPT5-RPT1 put the alarm in the repeat mode
of operation.
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 condi-
tion activates the IRQ/FT/OUT pin.
Note: If the address pointer is allowed to incre-
ment to the Flag Register address, an alarm con-
dition will not cause the Interrupt/Flag to occur until
the address pointer is moved to a different ad-
Figure 15. Alarm Interrupt Reset Waveform
Table 4. Alarm Repeat Modes
RPT5
1
1
1
1
1
0
ACTIVE FLAG
IRQ/FT/OUT
Table 4., page 17
RPT4
0Eh
1
1
1
1
0
0
shows the possible
RPT3
1
1
1
0
0
0
0Fh
RPT2
dress. It should also be noted that if the last ad-
dress 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 as shown in
sequent 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 Bat-
tery 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 M41ST84W was in the dese-
lect mode during power-up.
lustrates the back-up mode alarm timing.
1
1
0
0
0
0
RPT1
1
0
0
0
0
0
HIGH-Z
10h
Figure 16., page 18
Once per Second
Once per Minute
Once per Month
Alarm Setting
Once per Hour
Once per Year
Figure
Once per Day
AI03664
M41ST84W
15.. A sub-
17/29
il-