BackEvent Marker Input to Geode
8 Aug 2022
Consult Geode Serial Port Pinouts and Functions if needed.
The GPS/GNSS receiver in your Geode outputs NMEA-0183 messages automatically at regular intervals. External events can also create messages. When you want to distinguish between a regularly occurring message and a message created by an external event, look at the time stamp. Messages that are triggered by external events can be identified by their extra long time stamp, which includes a decimal showing the fractions of the second. You will see these long timestamps in GGA and GNS messages as highlighted in the following example message:
$GPGGA,214237.69325573,4145.74563492,N,11151.73747816,W,1,26,0.5,1362.906,M,-17.054,M,,*65
The second element of the message is the UTC time and is usually formatted as hhmmss.ss. In the example above, the time stamp includes the fractions of the second out to eight decimal places. This extremely precise time stamp is your indication that an external event occurred. (Regularly scheduled messages occur on the whole second mark or a specific fraction of a second that is predictable based on your set data rate, e.g., 214238.00.)
An Example
Here is a log of the GGA messages received by a Geode GNS2. During this time, an operator applied two +5V to pin 4. You can see these external events marked in the log by the long time stamps in the sixth and eight rows of the following table.
| Message Name | UTC Time hhmmss.ss | Latitude ddmm.mmmm | Hemi-sphere | Longitude ddmm.mmmm | Hemi-sphere | Cor-rection status | Sate-llites | HDOP | Altitude MSL | Units | Geoid separation | Units | Cor-rection age | correction source and checksum |
| $GPGGA | 151438 | 4145.74546341 | N | 11151.72932408 | W | 2 | 22 | 0.6 | 1365.628 | M | -17.054 | M | 5 | 0131*4C |
| $GPGGA | 151439 | 4145.74546042 | N | 11151.72933075 | W | 2 | 22 | 0.6 | 1365.623 | M | -17.054 | M | 6 | 0131*4A |
| $GPGGA | 151440 | 4145.74545874 | N | 11151.72933607 | W | 2 | 22 | 0.6 | 1365.616 | M | -17.054 | M | 7 | 0131*4E |
| $GPGGA | 151441 | 4145.74545654 | N | 11151.72934092 | W | 2 | 22 | 0.6 | 1365.612 | M | -17.054 | M | 7 | 0131*4A |
| $GPGGA | 151442 | 4145.74545294 | N | 11151.72934605 | W | 2 | 22 | 0.6 | 1365.613 | M | -17.054 | M | 7 | 0131*48 |
| $GPGGA | 151442.25213 | 4145.74545273 | N | 11151.72934811 | W | 2 | 22 | 0.6 | 1365.611 | M | -17.054 | M | 7.3 | 0131*44 |
| $GPGGA | 151443 | 4145.74544865 | N | 11151.72935097 | W | 2 | 22 | 0.6 | 1365.611 | M | -17.054 | M | 4 | 0131*41 |
| $GPGGA | 151443.6355 | 4145.74544530 | N | 11151.72935344 | W | 2 | 22 | 0.6 | 1365.611 | M | -17.054 | M | 4.7 | 0131*42 |
| $GPGGA | 151444 | 4145.74544489 | N | 11151.72935610 | W | 2 | 22 | 0.6 | 1365.611 | M | -17.054 | M | 5 | 0131*40 |
| $GPGGA | 151445 | 4145.74544049 | N | 11151.72935904 | W | 2 | 22 | 0.6 | 1365.61 | M | -17.054 | M | 6 | 0131*41 |
| $GPGGA | 151446 | 4145.74543844 | N | 11151.72936344 | W | 2 | 22 | 0.6 | 1365.606 | M | -17.054 | M | 7 | 0131*4B |
| $GPGGA | 151447 | 4145.74543550 | N | 11151.72936745 | W | 2 | 22 | 0.6 | 1365.606 | M | -17.054 | M | 7 | 0131*47 |
