INT 1A,4 - Read Real Time Clock Date (XT 286,AT,PS/2)

AH = 04

on return:

CH = century in BCD (decimal 19 or 20)

CL = year in BCD

DH = month in BCD

DL = day in BCD

CF = 0 if successful

= 1 if error or clock not operating

- calling this interrupt will update the DOS maintained date and

reset the ~BIOS Data Area~ date rollover flag at 40:70

- see ~RTC~