Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 193 of 265
The Controller only synchronises its minutes and seconds from the GPS Clock. The
date and hour are not ‘adjusted’ because the GPS Clock returns ‘UTC’ time
(Coordinated Universal Time), which does not take time zones or daylight saving in
to account. The user is responsible for setting the clock to approximately local time,
which the controller will then adjust using the minutes and seconds from the GPS
Clock. If daylight changes to the controller’s clock are required, the controller must
still be set-up as normal, see the handset commands BSA and CKA.
The Controller will not consider synchronisation if its clock is not been set-up, e.g.
the fault ‘FLF 7:255 RTC’ is set.
The Controller will only synchronise its time with the GPS clock once an hour. The
Controller's crystal clock (CTS=2) will easily maintain synchronisation over the hour.
The Controller will postpone the synchronisation if its time is within one hour of the
time of the previous synchronisation. The handset command CKS shows the date
and time of the last synchronisation and can be used to force a synchronisation.
The Controller will postpone synchronisation if the GPS Clock indicates that its time
is ‘not available’, see the CKM handset command.
The Controller will also postpone synchronisation while the GPS time and the
Controller time are ‘opposite sides’ of the hour, e.g. Controller Time = ‘XX:59:00’
and GPS Time = ‘YY:01:00’. In this case, synchronisation will occur when both
clocks ‘pass’ the hour mark, e.g. at ‘XX:00:00’ and ‘YY:02:00’. This is to avoid any
problems related to the fact that the hour part of the time is not used.