Expects: AH    04H
Returns: AH    0
CH    century, in BCD  (19H ... 20H)
CL    year, in BCD     (00H ... 99H)
DH    month, in BCD    (i.e., 01H=Jan ... 12H=Dec)
DL    day, in BCD      (00H ... 31H)
CF    NC (0) clock operating
CY (1) clock not operating or busy being updated
Info: Obtains the current date from the battery-backed CMOS Real-Time

Return values are in BCD ; for instance, CX = 1998H = 1998.

The BIOS avoids reentrancy by not returning the date 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 2aH (get system date)
- -

INT 1aH 04H: Read Date from Real-Time Clock