GN_Gmt, Get (read) machine system time in internal format

IN:
     C = Least significant byte of system date from last GN_Gmd call.
     (optional)
     DE = 0, not allowed.
     DE = 1, not allowed.
     DE = 2, return system time in ABC.
     DE > 255, pointer to write system date at (DE)

OUT:
     Fz = 0, C(in) is inconsistent with input parameter.
     Fz = 1, C(in) is consistent with time read
     DE, DE = DE(in) if DE < 255, else DE = DE(in) + 3
     ABC, ABC = ABC(in) if DE > 255 else contains the result

Registers changed after return:
     ......HL/IXIY same
     AFBCDE../.... different