SM8578 Nippon_Precision_Circuits America, SM8578 Datasheet - Page 14

• Manufacturer Part Number: SM8578
• Description: Real-time Clock IC
• Manufacturer: Nippon_Precision_Circuits America

Alarm Interrupt
Alarms can be set for day, day-of-week, hour, and minute. Also, multiple day-of-week alarms can be set.
It is recommended that the AF bit and AIE bit be initialized to “0” to avoid unexpected hardware interrupts dur-
ing the alarm setting procedure. Subsequent alarm data can be set and then the AF flag can be reset to zero for
reliable initialization. Then the AIE bit should be set to “1”. If hardware interrupts are never used, the AIE
should be set to “0” and the AF bit should be monitored using software as necessary.
Example 1) Alarm output for 6pm tomorrow:
Example 2) Alarm output for 6am every day excluding Saturday and Sunday:
Interrupt Output (INTN)
I
I
Timer interrupt output
Alarm interrupt output
Arbitrary frequency output
Output disabled
• Write “0” to AIE bit, and “0” to AF bit.
• Write “1” to day alarm AE bit.
• Write register 3’s current day-of-week data left-shifted by 1 bit into the day-of-week alarm register.
• Write “18h” to the hour alarm register.
• Write “00h” to the minute alarm register.
• Reset the AF bit to zero.
• Write “1” to the AIE bit.
• Write “0” to AIE bit, and “0” to AF bit.
• Write “1” to day alarm AE bit.
• Write “3Eh” to the day-of-week alarm register.
• Write “06h” to the hour alarm register.
• Write “00h” to the minute alarm register.
• Reset the AF bit to zero.
• Write “1” to the AIE bit.
The INTN output mode can be selected, by internal mode setting, for timer interrupt output, alarm interrupt
output, or arbitrary frequency output.
The output mode setting is set by the TIE, AIE, and FE bits as shown in the following table.
Note that multiple “1” bits are invalid.
If bit 6 in register 3 is “1”, left shift into the fr bit is not allowed. Instead, write “01h” (Sunday).
Mode
TIE
1
0
0
0
SM8578BV
Bit
AIE
0
1
0
0
NIPPON PRECISION CIRCUITS INC.—14
FE
0
0
1
0