[AT]
Expects: AH    02H
                                                                  
Returns: AH    0
AL    hours, in BCD 
CH    hours, in BCD
CL    minutes, in BCD
DH    seconds, in BCD
DL    00h = no Daylight Savings Time option
01h = Daylight Savings Time option
CF    NC (0) clock operating
CY (1) clock not operating or busy being updated
                                                                  
Info: Obtains the current time from the battery-backed CMOS Real-Time
Clock.

Return values are in BCD  in 24-hour format; for instance,
CX = 1234H = 12:34pm.

The BIOS avoids reentrancy by not returning the time if the clock
happens to be in the process of being updated.  Thus, if CF is
set on return, you should try a few more times before giving up.

See Also: INT 1aH (BIOS Time I/O)
DOS fn 2cH (get system time)
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INT 1aH 02H: Read Time from Real-Time Clock