Instruments with an NMEA interface can exchange data with other instruments, such as a GPS delivering position information to an autopilot. An instrument that delivers data is called a talker, while an instrument that receives data is called a listener. The current NMEA specification provides the possibility to connect one talker to up to four listeners. There is no provision however, to connect more than one talker to one or more listeners. It is thus impossible to connect both a log and a GPS to an autopilot or PC. The MiniPlex-41USB circumvents this limitation by offering four listener ports, one USB port and two talker ports.
The MiniPlex-41 is a four channel multiplexer, connecting up to four nautical instruments to each other and a PC, through the USB port. Many new laptops do not have a serial port anymore. One could use a USB <-> RS-232 converter but the logical choice is a multiplexer that connects directly to the USB port of your computer. The MiniPlex-41USB is supplied with drivers that create a virtual COM port, enabling all existing software to use the MiniPlex-41USB. Now a system can be built with up to four talkers and up to eight listeners. The PC can also act as a talker/listener, without sacrificing the number of allowed talkers. Incoming data is buffered and retransmitted as complete NMEA sentences to the connected instruments and PC. From the PC, NMEA data can also be sent to the instruments.