System clock, in the following format:
octet 0: seconds after the minute [0-60]
octet 1: minutes after the hour [0-59]
octet 2: hours since midnight [0-23]
octet 3: day of the month [1-31]
octet 4: months since January [0-11]
octet 5: years since 1900
octet 6: days since Sunday [0-6]
Setting this object requires valid value in octets 0 to 5,
and zero in octet 6. System clock can be disabled by setting
zero to all octets.