[ntp:questions] GPS and NTP Server

Paul.Croome at softwareag.com Paul.Croome at softwareag.com
Fri Feb 1 10:11:35 UTC 2008

Hallo Noosh,

I look after a Hopf 6855, which is similar to your 6842 but
receives LF signals from DCF77.

I configured my Hopf clock as follows:
Serial output: 09600 bits/sec, 8 data bits, no parity, 1 stop bit, no
Mode byte 1: binary 0100 0000
Mode byte 2: binary 0000 0000
Status and pulse output: binary 0000 0010

Then I wired up a TTL-to-RS232 level converter to the PPS
signal from the Hopf clock, and routed it to the DCD pin on
the serial output connector.

Make sure that your NTP is compiled with the refclock
drivers 22 (PPS clock discipline) and 38 (Hopf serial).

ntp.conf might look something like this:

server iburst
fudge time1 -0.005
server iburst prefer
fudge time1 -0.04
fudge flag1 1

When all this is working, the NTP software will read the
data strings and also the PPS signals from the Hopf clock
once per second and use this information to synchronize your
server's system clock. For more details, see Dave Mill's
excellent pages at


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