5.5 DCF77 Emulation
The clock generates TTL level time marks (active HIGH) which are compatible with the time marks spread by
the German long wave transmitter DCF77. This long wave transmitter installed in Mainflingen near Frank-
furt/Germany transmits the reference time of the Federal Republic of Germany: time of day, date of month and
day of week in BCD coded second pulses. Once every minute the complete time information is transmitted.
However, the generates time marks representing its local time as configured by the user, including announce-
ment of changes in daylight saving and announcement of leap seconds. The coding sheme is given below:
M
Start of Minute (0.1 s)
R
RF Transmission via secondary antenna
A1
Announcement of a change in daylight saving
Z1, Z2
Time zone identification
Z1, Z2 = 0, 1:
Daylight saving disabled
Z1, Z2 = 1, 0:
Daylight saving enabled
A2
Announcement of a leap second
S
Start of time code information
P1, P2, P3
Even parity bits
0
10
20
30
40
50
R
M
1
4
2
1
20
10
8
4
2
1
P
2
0
2
0
1
8
4
2
1
2
4
8
10
1
2
4
8
10
2
0
4
0
8
0
3
P
A1
Z1
Z2
A2
S
1
2
4
8
1
0
2
0
4
0
1
P
Minute
(reserved)
Hour
Day of Month
Day of Week
Year of the Century
Month of Year
Time marks start at the beginning of new second. If a binary "0" is to be transmitted, the length of the
corresponding time mark is 100 msec, if a binary "1" is transmitted, the time mark has a length of 200 msec. The
information on the current date and time as well as some parity and status bits can be decoded from the time
marks of the 15th up to the 58th second every minute. The absence of any time mark at the 59th second of a
minute signals that a new minute will begin with the next time mark. The DCF emulation output is enabled
immediately after power-up. The time stamps can be provided via pulses outputs. Furthermore, the DCF77
signal is available via a BNC connector as an amplitude-modulated 77.5 kHz carrier. This output can be used
for radio clocks as a replacement for a DCF77 antenna.
24
Date: 19th January 2021
GNS165DHS / GNS165DAHS