Logging of time event data from Ashtech GPS

RV "Maria S. Merian" OBS Survey
January 2007

University of Bergen (UoB)
Dept. of Earth Science
Allé gt. 41, N-5007 Bergen, Norway
Tel: (+47) 5558 3600
Fax: (+47) 5558 3660

1. Start "Ashtech" Hyperterminal session, and confirm some important settings

A Hyperterminal shortcut icon has already been made and placed on the desktop. Double-click this icon:

The Hyperterminal program will first ask some silly questions. Press Cancel:

And you need to confirm cancel:

It seems unwilling to give up, but just press OK:

Now, at last, you are allowed to enter the program. Notice information in the status bar below: You are connected, and parameters are 9600, 8-N-1:

To be able to communicate with the Ashtech GPS, some settings are crucial. Confirm these settings by selecting "Properties":

Select the "Settings" tab:

Then select "ASCII Setup ...":

Ensure that "Send line ends with line feeds" and "Echo typed characters locally" are selected, then press OK:

2. Setup Ashtech GPS

First reset the GPS, by issuing the $PASHS,RST command. The GPS will respond with a confirmation message "$PASHR,ACK*3D" for every valid command. Note that in the first case below, there was a typo, and even if you press Backspace and correct the error, Ashtech GPS still will not accept the command. It then says: "$PASHR, NAK*30".

Now enter the following commands. Ensure you receive "$PASHS,ACK*3D" on everyone.

Command	Explanation
$PASHS,SYS,MIX	Set receiver in mixed GPS/GLONASS mode
$PASHS,PEM,5	Set satellite elevation mask to 5 degrees (satellites lower then this is ignored).
$PASHS,PHE,F	Set event marker signal (i.e. GUNCO "FTB Scope" signal) to falling edge.
$PASHS,NME,TTT,C,ON	Output Event marker message on port C
$PASHS,TSC,GPS	Output Event marker time in GPS-system-time. Current difference between GPS and UTC time is 14 seconds. GPS time is leading.
$PASHS,NME,GGA,C,ON	Send NMEA message GGA on port C See two pictures below.

After you see that timestamping works as expected, activate the NMEA GGA sentence so that we also receive location information. Write $PASHS,NME,GGA,C,ON:

3. Capture data to file

Select Transfer -> Capture Text ..., as shown below:

Provide a filename. Remember to give ".txt" extension:

If you want to stop logging, select Transfer -> Capture Text -> Stop:

You must confirm data capture to file, using Windows Explorer (shortcut icon should already be on desktop):

Just open the file:

Notice how the difference between GPS- and UTC time manifests itself. GUNCO shot events are given in GPS time, and the $GPGGA time is in UTC. Current difference is 14 seconds: