Meinberg GEN170TGP User Manual

Technical Information

Operating Instructions

GEN170TGP

Impressum

Meinberg Funkuhren GmbH & Co. KG
Lange Wand 9
D-31812 Bad Pyrmont

Telefon: [phone] / 9309-0
Telefax: +49 (0) 52 81 / 9309-30

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

17. November, 2008

Index

Impressum ............................................................................................ 2

The Modular System GEN170TGP ..................................................... 5

General Information about DCF77 ....................................................... 6

GEN170 ............................................................................................... 7

GEN170 Overview ..................................................................... 7

The GEN170 Front Panel Layout ........................................................ 8

FAIL LED and LOCK LED ...................................................... 8

LC Display .................................................................................. 8

MENU Key................................................................................. 8

CLR/ACK Key ........................................................................... 8

NEXT Key.................................................................................. 8

INC Key...................................................................................... 8

The Menus in Detail ............................................................................. 9

Root Menu .................................................................................. 9

Menu SETUP ..................................................................................... 10

SETUP INITIAL TIME ........................................................... 10

ADJUST SECONDS ............................................................... 10

SETUP TIME ZONE ............................................................... 11

SETUP DAYLIGHT SAV ON/OFF ....................................... 11

SETUP LEAP SECOND ......................................................... 11

SETUP SERIAL PORT PARM............................................... 12

SETUP SER. STRING TYPE ................................................. 12

SETUP SERIAL OUTPUT ..................................................... 13

SETUP TIMECODE OUT ...................................................... 13

INIT USER PARMS ................................................................ 14

Resetting Factory Defaults ........................................................ 14

Firmware Updates ..................................................................... 14

Format of the Meinberg Standard Time String .......................... 15

Time code ........................................................................................... 16

Principle of Operation ............................................................... 16

Block Diagram Time code ........................................................ 16

IRIG Standard Format ............................................................... 17

AFNOR Standard Format ......................................................... 18

Assignment of CF Segment in IEEE1344 mode ....................... 19

Generated Time codes ............................................................... 20

Selection of Generated Time Code .................................. 21

Outputs ............................................................................ 21

AM Sine Wave Output .................................................... 21

PWM DC Output............................................................. 21

Technical Data ................................................................. 21

Technical Specifications GEN170 ..................................................... 22

Signal Description GEN170 .............................................................. 24

Rear Connector Pin Assignments GEN170 ........................................ 25

DCF77-Simulator ............................................................................... 26

Function .................................................................................... 26

Technical Specifications SIM77PV4......................................... 27

Rear Connector Pin Assignments SIM77PV4........................... 28

GEN170TGP Rear view ........................................................... 29

Assignments of the 25 pin Connector........................................ 29

4

The Modular System GEN170TGP

GEN170TGP is a set of equipment composed of a DCF77 generator GEN170 and a
DCF77 simulator SIM77PV4 together with a power supply, all installed in a metal
desktop case and ready to operate. The interfaces and signals provided by GEN170 and
SIM77PV4 are accessible via connectors in the rear panel of the case. Details of the
components are described below.

FAIL LOCK

CLR

ACK

NEXT INC

MENU

GEN170 assembled in desktop case

5

General Information about DCF77

The long wave transmitter DCF77 is installed in Mainflingen near Frankfurt/Germany
and transmits the reference time of the Federal Republic of Germany. This 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. The highly
accurate 77.5 kHz carrier frequency of DCF77 is modulated in both amplitude and
phase.

At the beginning of every second the amplitude of the 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.

The amplidude modulation can be easily decoded by a simple receiver circuit.
However, decoding the phase modulation achieves much more accuracy but also
requires much larger efforts including usage of correlation techniques.

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

Z1,Z2 = 1,0: Daylight saving enabled

A2 Announcement of a leap second

S Start of time code information (0.2 sec)

P1, P2, P3 Even parity bits

6

GEN170

GEN170 Overview

FAIL LOC K

The time code generator GEN170 has been
designed to generate all signals required to control or
simulate a DCF77 compatible long wave transmitter,
or provide the reference time for an NTP server:

o 77.5 kHz carrier frequency

MENU

CLR

ACK

NEXT INC

o second marks to modulate the carrier's
amplitude

o PRN sequence and PRN window to modulate
the carrier's phase

o Pulse-per-Second (PPS) output

Additionally, an IRIG or AFNOR time code signal is generated, and a serial time
string can be transmitted which includes the generated absolute date and time.

All signals are derived from a single 10 MHz reference frequency. That frequency can
either be generated by a high quality on-board oscillator, or it can be supplied externally.
The frequency source is selected by a jumper on the printed circuit board. The leading
edge of the second marks can be synchronized by an external PPS input signal.

Internal date and time is always based on UTC (Universal Time, Coordinated;
formerly GMT, Greenwich Mean Time). A configurable time offset can be applied to the
UTC time base to compute a local standard time. Beginning and end of a period of
daylight saving time can either be computed year by year based on a simple, configurable
algorithm, or can be configured for the current year. GEN170 generates the proper
changeover announcement flags as required by the DCF77 coding scheme.

Additionally, a date for insertion of a leap second can be configured. Actually, leap
seconds are only inserted at UTC midnight. GEN170 automatically generates the coding
sequences to announce the leap second as required for DCF77 and NTP, and also inserts
the leap second correctly.

16 TTL level inputs are provided to configure the length of the AM marks transmitted
in seconds 0 through 15 of a minute in DCF77 emulation. These second marks are
reserved by the PTB and are igno*red by most DCF77 receivers.

7

The GEN170 Front Panel Layout

FAIL LED and LOCK LED

The red LED labeled FAIL is turned on after power-up and stays on until the current
time has either been acknowledged via the ACK key in the front panel, or the time has
been set via the serial interface. The green LOCK LED reflects the generated DCF77
compatible AM time marks.

LC Display

The 4 x 16 character LC display is used to show the system's time and 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.

MENU Key

This key lets the user step through several display menus showing specific data.

CLR/ACK Key

This key has to be used when parameters are to be modified. When this key is pressed
the parameters that have been edited are saved in the battery buffered memory. If the
menu is left without pressing CLR/ACK all changes are discarded.

NEXT Key

When editing parameters (LCD cursor is visible) this key moves the cursor to the next
digit rsp. to the next parameter to be edited. If the current menu just displays data (cursor
not visible) pressing this key switches to a submenu (if available).

INC Key

When editing parameters this key increments the digit or letter at the cursor position.

8

The Menus in Detail

Root Menu

The root menu is shown when the receiver has completed initialization after power­up. During power-down the current date and time are kept in a battery buffered on-board
real time clock (RTC), so after power-up the initial calendar date and time should be
fairly correct. However, the red FAIL LED is on and a message is displayed asking to
acknowledge the initial time:

Unless the initial time is acknowledged by either pressing the CLR/ACK key in the
front panel or by setting the initial time via the RS-232 serial port the device stays in state
“unsynchronized“. This is to prevent the device from starting to distribute a wrong time
after power-up, which could otherwise happen due to interferences between an
incoming PPS pulse and the second changeover of the built-in RTC chip.

Once the initial time has been acknowledged the main menu is displayed. The first line
simply shows the module's function:

The next two lines display the current day of week, date, the name of the time zone
(just informational, as defined in the setup menu), and local time. The last line shows,
from left to right, the input levels of the control lines for the AM second marks 0 through

15. If a '1' is displayed a long time mark is generated at the corresponding second of a
minute, if a '0' is displayed, there will be a short mark at the corresponding second.

If the NEXT key is pressed in this menu, the display shows the module's firmware
version:

9