Meinberg DCF77C51 User Manual

FUNKUHREN

Technical Information
Operating Instructions

DCF77C51

Werner Meinberg
Auf der Landwehr 22
D-31812 Bad Pyrmont

Telefon: ++49 52 81 - 9309-0
Telefax: ++49 52 81 - 9309-30

Internet : http://www.meinberg.de
E-Mail : [e-mail]

May 28, 2002

Table of Contents

General Information about DCF77.............................................. 5

DCF77C51................................................................................... 7

Overview ..................................................................................... 7

Antenna and LF Receiver.............................................. 7

Microprocessor Circuit..................................................7

Buffered Real Time Clock ............................................ 7

Asynchronous Serial Port..............................................7

Installation ................................................................................... 8

Serial Port .................................................................................... 9

Serial Input and Output Drivers .................................... 9

Transmission Speed....................................................... 9

Framing ....................................................................... 10

Output mode ................................................................ 10

Time Zone ...................................................................10

Pulse Outputs............................................................... 10

DIL-Switches............................................................................. 11

Technical Specifications............................................................ 12

CE Label...................................................................... 13

Format of the Meinberg Standard Time String...........14

Connectors...................................................................15

DSUB-25 Connector Pin Assignments ....................... 15

Component Layout ...................................................... 17

Usage of the Current Loop Interface........................... 18

Active Output to Passive Input ..................... 18

Passive Output to Active Input ..................... 19

General Information about DCF77

The radio remote clocks made by Meinberg receive the signal from the long wave
transmitter DCF77. This long wave transmitter installed in Mainflingen near Frank­furt/Germany transmits the reference time of the Federal Republic of Germany. This
time reference is either the Central European Time (Mitteleuropäische Zeit, MEZ) or
the Central European Summer Time (Mitteleuropäische Sommerzeit, MESZ). The
transmitter is controlled by the atomic clock plant at the Federal Physical Technical
Institute (PTB) in Braunschweig/Germany and transmits the current time of day, date
of month and day of week in coded second pulses. Once every minute the complete
time information is available.

At the beginning of every second the amplitude of the high precision 77.5 kHz
carrier frequency is lowered by 75% for a period of 0.1 or 0.2 sec. The length of these
time marks represent a binary coding scheme using the short time mark for logical
zeroes and the long time mark for logical ones. 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.

Our radio remote clocks decode the highly accurate information on date and time
within a wide range around Germany. So some of our clocks are installed in Bilbao/
Spain as well as in the city of Umeå in northern Sweden - fully satisfying the
requirements of the users. The radio remote clocks automatically switch to summerti­me and back. The reception of the time information is free of charge and does not need
to be registered.

Generally it is important to position the antenna in an optimal way. It should be
mounted at least 30 centimeters away from the clock unit and from solid steel. The
antenna should be aligned at a right angle to the direction of the transmitter (Frank­furt).

Figure: Decoding Scheme

M Start of Minute (0.1 sec)
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 (MEZ)

Z1,Z2 = 1,0: Daylight saving enabled (MESZ)
A2 Announcement of a leap second
S Start of time code information (0.2 sec)
P1, P2, P3 Even parity bits

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