OS_Ht, Hardware time manipulation

IN:
     A = HT_RES ($01), reset hardware timer
         HL = pointer to a 5 bytes buffer
     A = HT_RD ($02), read hardware timer
	 A = HT_UPT ($03), read uptime

OUT:
     A(in) = HT_RES ($01)
		 -
     A(in) = HT_RD ($02)
		 BHL = pointer to a 11 bytes time system buffer
	 A = HT_UPT ($03)
		 BCD = minutes, E = seconds since latest hard reset

Registers changed after return:
     A.BCDEHL/IXIY same
     .F....../.... different

IN:  A = HT_MDT ($03), read monthy/date/time address
OUT: Fc = 0
     BHL = month, date, time address

Registers changed after return:
     ...CDE../IXIY same
     AFB...HL/.... different