Raymarine NMEA Multiplexer GPS Receiver User Manual

Real-time or buffered inputs
Before connecting NMEA inputs to your NMEA Multiplexer,
consider whether they should be connected as real time or
buffered inputs:
Data running at a fast rate and consisting of single sentences,
particularly time-critical data, should be connected to either
NMEA In 1 or NMEA In2, real time inputs. This includes
data from devices such as Fast Heading Sensors, and Fluxgate
Compasses. When data is processed in real time, some sen-
tences may be lost, but the timing of the data is maintained
and there is no time delay. These inputs will store only one
NMEA sentence at a time, and thus prevent unwanted delays.
Slower data that is input as a burst should be connected to
either NMEA In 3
or NMEA In 4, as buffered inputs. This
includes data such as GPS, route and depth information, for
which the timing is less critical. These inputs can store multiple
sentences (12 to 70, depending on length). This is necessary
for devices such as GPS, which can output 10 sentences at
once, every 1 or 2 seconds.
Connect an unused pair of NMEA In a and b terminals on the
NMEA Multiplexer to the NMEA output port of each device from
which you wish to receive NMEA data. The manner in which the
connections are made depends on whether the device has a
differential or single ended output, as follows: