Meinberg VP100 20 - Manual (Page 7)

7
VP100/20 as Stand Alone Clock
After connecting the power supply the displayed time/date can be set by the two
buttons in the rear panel of the case. The accuracy of the time depends on the precision
of the internal quartz base.
An automatic changeover of daylight saving can be programmed as described in
section "Daylight Saving".
VP100/20 as Radio Clock
It is not possible to run this variant of the VP100/20 as a slave clock. The DSub
connector (IN) in the rear panel has no effect. The DSub connector (OUT) can be
connected to further VP100/20s or similar systems to run them as slave clocks.
An external ferrit antenna is used to receive the signal from DCF77 and supplies it
to the on-board LF receiver where it is demodulated by a synchronous detector with
automatic gain control. The demodulated time marks are fed to the clock´s micropro-
cessor.
The time marks from the receiver circuit are filtered and decoded by the micropro-
cessor system. Parity and consistency checks over a period of two minutes take care
for detecting errors in the received time string. The checked and decoded time is
written to the on-board real time clock and spread by the interfaces. A software
watchdog lets the microprocessor recover from malfunction. A power-fail comparator
resets the microprocessor if the supply voltage drops below a specified threshold.
In case of supply voltage failure the on-board real time clock keeps the time
powered by a lithium battery which has a live time of at least 10 years guaranteed.
After powering up the system the time keeped in the real time clock is displayed
immediately. A dot below the colons of the time on the display indicates the modula-
ted DCF77 signal. After synchronisation this dot dissappears, however, after loss of
reception for more than 6 hours the colons start flashing. If the antenna is installed
properly and the signal from DCF77 can be received without strong distortions, the
"Modulation Dot" starts blinking exactly once per second, corresponding to the time
marks from DCF77. For a better control an acoustic signal is added to the "Modulation
Dot" for 2.5 minutes.