M41T81MY6 STMICROELECTRONICS [STMicroelectronics], M41T81MY6 Datasheet - Page 18

• Manufacturer Part Number: M41T81MY6
• Description: Serial Access Real-Time Clock with Alarms
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

M41T81
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 M41T81 is in the bat-
tery back-up mode to serve as a system wake-up
call.
Bits RPT5-RPT1 put the alarm in the repeat mode
of operation. Table 11, page 19 shows the possi-
ble configurations. Codes not listed in the table de-
fault 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.
Figure 18. Alarm Interrupt Reset Waveform
Figure 19. Back-up Mode Alarm Waveform
18/28
V CC
IRQ/FT/OUT/SQW
V SO
ABE and AFE Bits
AF Bit in Flags
Register
IRQ/FT/OUT/SQW
ACTIVE FLAG
0Eh
HIGH-Z
0Fh
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-
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/SQW output is cleared by a
READ to the Flags Register as shown in Figure
18. 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 19 illustrates the back-up mode
alarm timing.
tREC
HIGH-Z
10h
HIGH-Z
AI04617
AI05663