Meinberg HSC509 - Manual (Page 9)

9
LF Receiver
An external ferrit antenna is used to receive the signal from DCF77 and supplies it to the
on-board direct conversion quadrature receiver with automatic gain control. The demo-
dulated time marks are fed t
o the clock´s microprocessor.
Microprocessor System
The time marks from the receiver circuit are filtered and decoded by the microproces-
sor system. Parity and consistency checks over a period of two minutes take care for
detecting errors in the received time telegram. 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. A
flash EPROM is used as program memory which can be loaded with the firmware by
the serial interface COM0.
LC Display
The 4 x 16 character LC display is used to show the receiver´s status and let the user
edit parameters. The keys described below let the user select the desired menu. The
next chapter lists all available menus in detail. A quick reference of the available
menus and submenus can be found at the end of this document.
Buffered Real Time Clock and RAM
In case of supply voltage failure the on-board real time clock keeps the time powered
by a backup capacitor for at least 100 hours. This capacitor does not need any
maintenance. The content of the RAM is buffered also. Alternatively, the clock can be
ordered with a lithium battery which has a live time of at least 10 years guaranteed.
Slave Clocck Pulses
The radio clock generates bipolar pulses to drive slave clocks. These DC isolated
pulses are generated on a second line and on a minute line. The drivers are short-
circuit protected. A short-circuit detection ensures generating the lost pulses after the
fault has been eliminated. So the slave clocks catch up the time automatically.