Meinberg C28COM User Manual
Technical Information
Operating Instructions
C28COM
Driver software for
Windows 95/98® operating systems
Impressum
Werner Meinberg
Auf der Landwehr 22
D-31812 Bad Pyrmont
Phone: ++49 52 81 - 9309-0
Fax: ++49 52 81 - 9309-30
Internet: http://www.meinberg.de
Email: info@meinberg.de
August 20, 2008
Table of contents
Impressum ............................................................................................ 2
General Information about DCF77 ...................................................... 5
Overview C28COM ............................................................................. 6
Installation ............................................................................................ 7
Power supply .............................................................................. 7
Aligning the antenna ................................................................... 7
Pin assignment of the 9pin D-SUB ...................................................... 8
Pin assignment of the computer’s RS232 ports ................................... 8
Status LED ........................................................................................... 9
Technical specifications C28COM ...................................................... 9
Format of the Meinberg standard time string ........................... 10
Housing/Dimensions ................................................................ 11
CE Label ................................................................................... 11
Diskette with driver software ............................................................. 12
Operation under Windows95/98® ..................................................... 13
Quick installation ...................................................................... 13
Detailed installation instructions .............................................. 14
The driver software MBGTIMEMON.EXE ...................................... 15
The pull-down menu „File“ ................................................................ 16
Options...................................................................................... 16
Advanced Options ........................................................... 17
Set time only if clock synchronous ................................. 17
Synchronization radius .................................................... 17
Number of correct telegrams ........................................... 18
Activate datalogger ......................................................... 18
Delete logfiles after * days .............................................. 19
Load program at systemstart ........................................... 19
View logfile .............................................................................. 19
Terminal.................................................................................... 20
Start/Stop timecontrol ............................................................... 20
Uninstall monitor ...................................................................... 20
Exit monitor .............................................................................. 20
Entries in the registry used by the time adjustment service ............... 21
4
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 represents 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.
Figure: Decoding scheme
5
5
Overview C28COM
The radio remote clock C28COM is designed to operate in conjunction with a serial
RS-232 interface of a computer. The supply voltage for the module is provided by
control signals of the COM port. Therefore no external voltage needs to be applied.
The module generates a serial Meinberg Standard String which contains informations
like date, time and status of the clock. C28COM sends this string once per second with
transmission speed 9600bd framing 7E2, see chapter „Format of the Meinberg standard time string“ for details.
An internal 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 straight detector with automatic
gain control. The demodulated time marks are fed to the clock´s microprocessor for
decoding. 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 software clock and spread by the serial interface of C28COM.
C28COM includes a two-color LED which displays the demodulated DCF77 time
marks and the status of the clock.
The clock is precanned with a connection cable of two meters length and is equipped
with a 9pin D-SUB female connector (25pin on request). It is appropriated to connect
directly to the RS-232 port of a PC.
The scope of supply includes a driver software for Windows95/98® operating
systems. This program adjusts the system time of the computer and displays several
status information of the time adjustment and the clock C28COM.
Meinberg driver software for various different operating system can be found for
free download at: http://www.meinberg.de/german/sw/index.htm
Note about using the driver software: the module C28COM doesn’t
include a real time clock. After power up the time string can’t
contain the current time until first synchronization therefore. If you
are using a Meinberg driver software, the option of accepting the
time send by the DCF-clock even in case of free run should not be
active.
6
Installation
After connecting the D-SUB connector to a RS-232 port of a computer the C28COM
is already installed. To ensure correct operation the following points have to be
considered.
Power supply
The flow control signals RTS (Request To Send) and DTR (Data Terminal Ready)
and the data signal TxD (Transmit Data) of the connected PC port are used to supply
the power needed by C28COM.
After powering up the computer the control signals do not conduct the required
potential. For this reason the C28COM is not ready to operate until the driver
software is started. The software switches the control signals to the correct state.
If the user wants to write his own software for evaluating the serial time string, he
has to make sure, that the software switches the flow control signals RTS and DTR of
the computer into the ‘OFF’-state. These lines must have a positive voltage relating to
the reference potential (GND).
Aligning the antenna
It is important that the position of the module and it’s integrated antenna ensures
optimal conditions for receiption of the DCF77-signal. The antenna should be aligned
with the arrow symbol printed on the case pointing to the direction of the transmitter
(Frankfurt am Main). A distance of several meters is recommended to all TVs or
computer monitors, computers or processorboards. The antenna should have a minimum distance of 30 centimeters from solid steel.
The alignment of the Antenna can be done with the help of the integrated LED. Like
described in chapter „General Information about DCF77“, the DCF77 protocol can
only be decoded if all time marks can be received correctly without interfering pulses.
Therefore a LED switched off strictly once per second (not in second 59) indicates
good conditions of receiption.
7
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