Specifications
ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 142 of 265
15.3.23 RTC Synchronisation (TS1)
A ‘TS1’ control bit may be programmed to cause the master time clock to be
synchronised at 8, 18, 28, 38, 48 or 58 minutes past each hour. The synchronisation
code is transmitted at 0101 levels, each level of 1-second duration.
The central office computer has to be programmed to send the synchronisation code
when its system clock indicates any of the times shown below. The central office
computer must be programmed such that the final “1” bit of the synchronisation code
is sent on the 30 second boundary, i.e. start sending code at 27 seconds past with
first ‘0’ bit.
Hour Minutes
Seconds
Any 08 30
Any 18 30
Any 28 30
Any 38 30
Any 48 30
Any 58 30
When the controller receives the second “1” bit (at the end of the code), it checks to
see if the real time clock is within 29 seconds of the synch time. If it is, the controller
sets the clock to 30.0 seconds past the minute. The hour is disregarded by the
controller check.
For example, if the synch code is sent at the time “06:08:30” and real time clock is
between “06:08:01” and “06:08:59”, it will be re-synchronised to “06:08:30” and the
confirm bit ‘CC1’ is activated, see section 15.3.24.
If the real time clock in the controller is more than 29 seconds out, i.e. the minutes is
not one of those listed above, e.g. the time in the controller is “06:09:02”, the
synchronisation code is ignored and synchronisation confirm (‘CC1’) is not returned.
15.3.24 RTC Synchronisation Confirm (CC1)
A ‘CC1’ reply bit may be returned to confirm the synchronisation of the RTC (see
section 15.3.23 above). The ‘CC1’ confirm signal is maintained for a pre-set period,
configurable in 1-second steps, but is normally set to 3 seconds. If the clock
synchronisation fails, the ‘CC1’ reply bit remains inactive.
15.3.25 Take Over (TO)
A ‘TO’ control bit may be programmed so that no ‘F’ bits will be effective unless ‘TO’
is present. The ‘TO’ can also be programmed to inhibit the local link to an adjacent
controller for example. Also see section 15.5.
15.3.26 Take Over Confirm (TOR)
A ‘TOR’ reply bit may be returned to indicate that UTC mode is active.