Hochschule Augsburg
NTP Service - DCF77
DCF77 Time Code
The carrier wave frequency of the german time code transmitter
DCF77 is 77.5 kHz in the low frequency (LF) band. It is
modulated by frequency (FM) and amplitude (AM). The latter is
the simplest way to decode the time signal.
Every second, the amplitude is dropped by 25% for 100 ms
or 200 ms. The dropping happens exactly on the second and
is used as time mark. The last mark in every minute is left off
to indicate the end of minute.
The pulse duration represents a bit value, 0 for the shorter
and 1 for the longer pulse. The 59 pulses of one minute form
the 59-bit DCF77 time code containing all necessary time and
date information.
Encoding:
Second Name Contents
---------------------------------------------------
00-10 AM: free, FM: 0
11-14 free
15 R alternate antenna
16 A1 expect DST change
17 Z1 daylight saving time
18 Z2 standard time
19 A2 expect leap insertion/deletion
20 S start of time code (always 1)
21-24 M1 minute ones [1,2,4,8]
25-27 M10 minute tens [10,20,40]
28 P1 minute parity (21-27)
29-32 H1 hour ones [1,2,4,8]
33-34 H10 hour tens [10,20]
35 P2 hour parity (29-34)
36-39 D1 day ones [1,2,4,8]
40-41 D10 day tens [10,20]
42-44 DW day of week (1: Mon -> 7: Sun) [1,2,4]
45-49 MO month ones [1,2,4,8]
50 MO0 month tens [10]
51-53 Y1 year ones [1,2,4,8]
54-57 Y10 year tens [10,20,40,80]
58 P3 date parity (36-57)
59 usually missing (minute indication),
except for leap insertion
Note:
- Numbers are BCD (binary coded decimals).
- The least significant bit comes first.
- Parity is even (even number of ones).
- Bits 16 and 19 are set 1 hour before event.
- No leap direction announcement.
- Only two digit year numbers.
1998-05-23