m41t81s STMicroelectronics, m41t81s Datasheet - Page 18

• Manufacturer Part Number: m41t81s
• Description: Serial Access Real-time Clock With Alarms
• Manufacturer: STMicroelectronics

Watchdog timer
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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/SQW output is cleared by a READ to the Flags Register as shown in
Figure
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 13. Alarm interrupt reset waveform
Figure 14. Back-up mode alarm waveform
Table 3.
The watchdog timer can be used to detect an out-of-control microprocessor. The user
programs the watchdog timer by setting the desired amount of time-out into the Watchdog
Register, address 09h. Bits BMB4-BMB0 store a binary multiplier and the two lower order
RPT5
1
1
1
1
1
0
13. A subsequent READ of the Flags Register is necessary to see that the value of
V
IRQ/FT/OUT/SQW
V
V
ABE and AFE Bits
AF Bit in Flags
Register
IRQ/FT/OUT/SQW
CC
PFD
SO
Alarm repeat modes
RPT4
ACTIVE FLAG
1
1
1
1
0
0
RPT3
0Eh
1
1
1
0
0
0
HIGH-Z
Figure 14
RPT2
1
1
0
0
0
0
illustrates the back-up mode alarm timing.
0Fh
RPT1
1
0
0
0
0
0
Once per Second
Once per Minute
Once per Month
Once per Hour
Alarm Setting
Once per Year
Once per Day
trec
HIGH-Z
10h
AI04617
AI09164b