AH = 04h: Read RTC Date

This function reads the date from the real-time clock.

• Input: AH = 04h
• Output: AH = 00h
  CH = Century in BCD:
  19h if 20th century
  20h if 21st century CL = Year in BCD
  DH = Month in BCD
  DL = Day in BCD

• Error conditions: Carry Set if the RTC data is invalid,
  otherwise Carry Clear

• Registers modified: AX, CX, DX, STATUS