Posts Tagged ‘GPZDA’

Enabling $GPZDA NMEA sentence on Adafruit Ultimate GPS

Tuesday, June 10th, 2014

I’ve been using an Adafruit Ultimate GPS module as a time source which with their standard GPS Library provides the $GPRMC NMEA 0183 sentence containing the time and date however I had a preference for the $GPZDA sentence for the simple fact it provides the year as four digits instead of only two.

This forum post suggested it was possible on the MTK3339 chip by sending an unsupported variant of the command that enables the various sentences:

$PMTK314,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0*29

However, this didn’t work. The datasheet provided by Adafruit doesn’t document the majority of the data fields in this command, just identifying them as reserved. I found another datasheet elsewhere which I think is just an older revision of the same document and this has slightly better information. In fact, the command was only slightly wrong, it’s in fact this:

$PMTK314,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0*29

It’s the 18th field, not the 17th as the forum post originally suggested. Sending this command to the GPS module now returns the $GPZDA NMEA sentence. It can be enabled with other sentences, you just need to update the XOR checksum after the * using something like this online tool.