MOD-GPS no $PMTK sentences?

[Dave]

Hi,

I'm having a communication problem with the MOD-GPS.  It appears to be alive (flashing red LED) and I'm correctly receiving $GPGGA, $GPGSV, $GPGSA, and $GPRMC sentences.  However, I never see any $PMTK sentences and it doesn't respond to any $PMTK requests.  I'm thinking I missed something subtle...

I noticed that my MOD-GPS looks different from the picture on the Olimex website - mine has a SiRF3 logo sticker.  However, it doesn't respond to any $PSRF requests either. 

Does anyone have any ideas before I scope the UART transmit?  (The UART believes it's transmitting OK but I haven't yet verified the signal at the UEXT connector.)


Thanks very much,
Dave

[MBR]

$PMTK is a MediaTek's proprietary extension of the NMEA protocol and works only with MTK chipsets, so if the chipset is really a SiRF III, it wouldn't work. Try the SiRF ones instead (and check if the baudrate of the serial port is in a sane range 4800 or 9600bps). Or, if you do it on Linux, try gpsd (http://www.catb.org/gpsd/), it's much easier to work with than the NMEA (which is ugly) and has nice tools for testing.

[Dave]

Hi MBR,

Thanks very much for your reply.  I did verify that my USART is transmitting (loopback at the UEXT pins) so it appears the problem is either the MOD-GPS cable (unlikely since the module has power and I'm getting the $GP... sentences) or this MOD-GPS really isn't either an MTK chip or a SiRFstarIII...WTF?

I guess I'm going to have to crack open the case and see what the chip really is...  The huge frustration is the lack of accurate/complete documentation on the MOD-GPS page.


Thanks again,
Dave