INT 1A,0 - Read System Clock Counter
AH = 00 on return: AL = midnight flag, 1 if 24 hours passed since reset CX = high order word of tick count DX = low order word of tick count - incremented approximately 18.206 times per second - at midnight CX:DX is zero - this function can be called in a program to assure the date is updated after midnight; this will avoid the passing two midnights date problem