Guralp Systems CMG-DCM build <10,000 - Manual (Page 91)

Operator's Guide
This is also the recommended configuration for CMG-DAS units,
where GPS reception is available.
8.2 Using NTP with CMG-DAS units
Where GPS reception is not practical but an internet connection is
available, NTP can be used to synchronise the Platinum clock, which
can then generate NMEA output. This NMEA data-stream can be fed
to the GPS input of the digitiser module using an external cable from a
serial port.
To configure the NTP subsystem, see section 6.3 on page 64.
To configure NMEA output, see section 8.6 on page 94.
8.3 Using GPS with Authenticated Digitisers
Güralp Systems Ltd's authenticated digitisers provide a CMG-DM24
and a CMG-EAM in a single package. An internal, bi-directional
November 2010 91
Note: RTSTATUS packets are available with MkIII DM24 units.
Earlier units, such as MkIIs, are not capable of generating these
packets.
Note: RTSTATUS packets are available with CD24 units
running firmware revision 279 and above.