Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 192 of 265
25.3 Timetable Resolution
CLF plans and timetable events are introduced by timetable settings to a resolution
of 1 second.
25.4 Daylight Saving
The RTC will advance or retard one hour at 02.00 hours on the date (usually a
Sunday) specified by the handset commands CKA and CKR. Once actioned the
date is updated by the controller to identify the same day in the following year.
Therefore, the dates do not need to be set-up every year, only on those years where
the required date is not the same Sunday but the Sunday in the following week.
When the clock is advanced, any CLF plan change or timetable event facility that
would have occurred between 2 a.m. and 3 a.m. will automatically be brought into
effect.
When the clock is retarded, a return to the conditions applicable at 1 a.m. is
automatically implemented.
25.5 Minute Pulse
This signal is of 5 seconds duration and begins 5 seconds before each 5-minute
boundary of the RTC. It is available to special conditioning and therefore may be
allocated to a normal ST900 output port bit or UTC reply bit. Conditioning bit goes
active for the duration of the pulse.
25.6 GPS Clock Kit
In areas where the stability of the mains’ frequency is unsatisfactory, the controller
can be fitted with a GPS unit from which the controller can obtain the current time,
keeping its clock synchronised.
This kit is Part Number 667/1/27014/000. The kit contains a GPS Antenna which
comes with approx. 30 feet of cable and a BNC connector. Fitting instructions are
available, see Drawing Number 667/CH/27014/000.
The controller is automatically synchronised to the GPS Clock. The GPS handset
commands CKM and CKS are defined in the Handset Handbook
(667/HH/32900/000).
IMPORTANT: It is recommended that the controller is switched from its default
mains synchronised clock to its crystal synchronised clock (using the handset
command CTS=2) if a GPS clock is fitted.
The Controller monitors the messages from the GPS Clock continuously; see the
handset command CKM for details.