Comtech EF Data CDM-570L Installation And Operation Manual page 449

This section briefly describes the new software feature that has been added to the
CDM-570/570L to permit a Furuno GP-320B GPS receiver to be connected to a distant-
end modem, and for the local end to query, via the EDMAC channel, the output from the
GPS receiver.
In order to do this, the local modem is set as MASTER, and the distant-end is set as
SLAVE. The Furuno GP-320B GPS receiver is connected to the remote control serial
port of the distant end modem.
NOTE: If 'standard' EDMAC framing is used, the MASTER can be a CDM-550,
CDM-600/600L, or CDM-570/570L. However, if EDMAC-2 framing is used, both ends
of the link need to be CDM-570/570L.
New remote commands sent to the SLAVE modem are used to retrieve GPS data
sentences. The modem has a circular buffer to contain the most recent 1000 characters
received from the GPS receiver, which is about 2-3 seconds of data. The method of
searching for the correct sentence is to simply look for the first match in the buffer. This
gives about two seconds' delay time in the worst case at the "slave" end, plus any delay
added by the EDMAC channel. When a query is actively taking place, the placing of new
GPS data into the buffer is temporarily suspended.
G.1 Hardware Setup:
1. Ensure that the serial remote control type of the SLAVE modem is set to RS232.
2. Follow the Setup sequence of EDMAC described in the CDM-570 product
3. Connect the GP-320B GPS receiver to the SLAVE modem's serial port. The
4. Establish an RF link between the SLAVE and MASTER modems, and once
Appendix G. GPS MODE
manual. The SLAVE Modem must be a CDM-570 or CDM-570L, and the
MASTER modem can be any modem compatible with the SLAVE modem.
YELLOW wire in the Furuno GPS cable (RDA) should be connected to pin 3 of
the CDM-570L serial remote control port (9 pin D-type male). Connect the
ground wire from the GPS to pin 1.
satisfied that both demods are locked, set up a serial communications session via
the serial port of the MASTER modem, and begin sending EDMAC messages to
the distant-end SLAVE.
G–1