Raymarine NMEA Multiplexer Especificaciones descargar pdf (Pagina 3)

Introduction

The MiniPlex-2Wi is an NMEA multiplexer that enables the connection of multiple NMEA 0183

instruments to each other and a computer and/or wireless devices. It is developed to solve a

fundamental problem with the NMEA 0183 standard.

The NMEA 0183 standard defines a communication protocol that enables navigation instruments to

exchange data with each other. A compass can send a bearing to a radar to enable a north-up

display, a GPS can send cross-track information to an autopilot in order to steer a programmed

course. The same GPS can also send information to the radar at the same time since the NMEA

0183 standard specifies that one device must be able to send data to up to four other devices.

NMEA data is made up of short text messages with a strict format called sentences and are human-

readable.

Talkers and Listeners

Communication using the NMEA 0183 protocol involves at least one

device that sends NMEA sentences and another device that receives

NMEA sentences. By convention, a sending device is called a talker

while a receiving device is called a listener. The picture on the right

shows such a minimal system: a gyrocompass sending heading

sentences to a radar.

The NMEA 0183 standard specifies that a talker should have enough driving capability to talk to

four listeners. This is as easy to achieve as telling a story to an audience of up to four people. The

only requirement is to talk loud enough.

The picture left below shows such a situation.

It gets complicated when several talkers must send data to one listener as shown in the picture on

the right. Unless that listener has multiple inputs, this is not possible without help. Simply

connecting talkers to one listener as shown is like four persons simultaneously telling you a

different story. You can make neither head nor tail of it. In electronics terms: the outputs of the

talkers will effectively short-circuit each other and the sentences they transmit will be corrupted.

This is where a multiplexer offers the solution.

The Multiplexer

A multiplexer, sometimes called ‘combiner’, has multiple inputs, each acting as a single listener

connected to a talker (the instruments). It has one or more outputs that are able to talk to multiple

listeners. These outputs deliver the combined data from the inputs.

A clever piece of software inside the multiplexer reads the NMEA sentences that are received on

the inputs simultaneously and stores them into queues, one for each input. Another part of the

software retrieves the sentences from the queues, one at a time, and sends them to the outputs of

the multiplexer. This way, four incoming streams of sentences are combined into one single

stream.

GPS

VHF

Radar

Auto-

pilot

GPS

Depth

Wind

Log

Gyro Radar

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