SECTION 6
Conversions and Interfaces
PEN*KEY
R
6100 Computer Programmer’s Reference Guide 6-99
INT 1Ah, Function AH = 06h: Set the Real-Time Clock Alarm
BIOS
If the alarm is currently enabled, the function is not performed. This function
writes the alarm hour, alarm minute, and alarm second data to the CMOS RAM
area of the MC 146818 and sets the AIE bit in Register B.
This function must wait for the updateĆinĆprogress bit to become zero and disable
interrupts before accessing CMOS data. Once activated, the alarm expires once
every 24 hours until deactivated. When the alarm expires, INT 4Ah is issued.
If the calling program needs control passed to it, it must place the address of the
interrupt handler in the vector for INT 4Ah. The user routine must save and reĆ
store all registers and preserve the state of the machine.
If the high two bits of the hour are set, an alarm expires every hour. If the high
two bits of the minutes are set, the alarm expires every minute. If the high two
bits of the seconds are set, the alarm expires every second.
The function must return with the carry flag set, if there was an error; otherĆ
wise, the carry flag must be cleared.
On Entry:
AH = 06h
CH = Hours in BCD (0ć23)
CL = Minutes in BCD (0ć59)
DH = Seconds in BCD (0ć59)
On Return:
None
INT 1Ah, Function Ah = 07h: Reset the Real-Time Clock Alarm
BIOS
Clears any pending alarm specified by INT 1Ah, Function 06h by resetting the
AIE bit in Register B.
On Entry:
AH = 07h
On Return:
None
INT 1Ah, Function AH = 09h: Read the Real-Time Clock Alarm
BIOS
Reads the alarm hour, alarm minute, and alarm second data and the AIE bit in
Register B from the CMOS RAM area of the MC 146818. This function must
wait for the updateĆinĆprogress bit to become zero and disable interrupts before
accessing the CMOS data.
The function must return with the carry flag set, if there was an error; otherĆ
wise, the carry flag must be cleared.
On Entry:
AH = 09h
On Return:
CH = Hours in BCD (0ć23)
CL = Minutes in BCD (0ć59)
DH = Seconds in BCD (0ć59)
DL = Alarm status
0 = Alarm not enabled
1 = Alarm enabled
6. Conversions and
Interfaces
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