The RTX Map Interface Device (MID) converts ARINC 429 data into RS232 data in NMEA format. Most commercially available mapping software or EFB software requires position information in NMEA format. The NMEA format is a series of ASCII strings that are easily read in and are understood by the software. However, most GPS devices do not output data in NMEA format, but instead output data in ARINC 429 format. The RTX-MID converts between ARINC 429 data, from a GPS, to RS232 (NMEA) data. The MID is very small, it has no internal batteries to be replaced or recharged, and it requires no external power supply (it uses a small amount of power from the RS232 port itself). The MID is a specialized version of our popular RTX ARINC 429 Serial Port Adapter and is specifically designed to convert ARINC 429 data to NMEA format.


The ARINC 429 input
The MID will read and process the following ARINC 429 labels:


125,150 Greenwich Mean Time
147 Magnetic Variation
203,204,076 Altitude
260 Date
310,110 Present Position Latitude
311,111 Present Position Longitude
312,112 Ground Speed
313 True Track Angle
314 True Heading
320 Magnetic Heading

The MID will sense the incoming ARINC 429 data rate (high speed or low speed) and will adjust itself automatically. There is no setup required.


The RS232 output
The RTX SPA-MID will begin transmitting as soon as it is plugged into an RS232 port. Once per second, the RTX SPA-MID will output to the RS232 port 5 NMEA sentences ( $GPRMC, $GPGGA, $GPGLL, $GPVTG, and $PGRMZ) with the most recent data for each field. There are multiple fields in each sentence. Each field is separated by a comma (,). Some of the fields (e.g. Latitude and Longitude) have a comma within the field. If some of the ARINC 429 data is missing or is older than 3 seconds, the associated field in the appropriate sentence will be sent as a blank.

The RTX SPA-MID will work with any computer running any operating system. The RTX SPA-MID requires no special device drivers, it uses the same RS232 device driver that comes with the computer. If there is no RS232 port available, the RTX SPA-MID will also work with a USB port (with an adapter).






ARINC 429 to RS232 (NMEA)
Map Interface Device