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AH = 02h CF clear to avoid bug (see below)
Return:
CF clear if successful CH = hour (BCD) CL = minutes (BCD) DH = seconds (BCD) DL = daylight savings flag (00h standard time, 01h daylight time) CF set on error (i.e. clock not running or in middle of update)
Notes: This function is also supported by the Sperry PC, which predates the IBM AT; the data is returned in binary rather than BCD on the Sperry, and DL is always 00h. MS-DOS/PC DOS IO.SYS/IBMBIO.COM use this function to detect if a RTC is preset by checking if the returned values are non-zero. If they are, this function is called one more time, before it is assumed that no RTC is present.
BUG: Some BIOSes leave CF unchanged if successful, so CF should be cleared before calling this function
See Also: AH=00h - AH=03h - AH=04h - INT 21/AH=2Ch
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