Casio IT-2000D - Manual (Page 49)

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2.3.7 Clock Timer
Clock BIOS
00h to 07h of the INT1Ah function are compatible with the IBM PC/AT.
Since INT1Ah can be called in the C language, an alarm operation using the clock can be set with
the system library.
Alarm
If an alarm operation is set using the INT1Ah or system library, it is possible to cause an INT4Ah
interrupt at the specified time to issue the alarm. Normally a buzzer sounds if an INT4Ah occurs,
however, the application program side can hook this interrupt and perform its unique alarm process.
It is also possible to automatically turn on the power at the specified alarm time by means of the
system library (refer to Chapter 7.6.2 “System Library”).