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1300 Henley Court Pullman, WA 99163 509.334.6306 www.digilentinc.com PmodGPS™ Reference Manual Revised April 12, 2016 This manual applies to the PmodGPS rev. A Overview The PmodGPS can add satellite positioning accuracy to any embedded system. The PmodGPS features a GlobalTop FGPMMOPA6H GPS antenna module that utilizes the MediaTek GPS MT3329. Features include:         Ultra-sensitive GPS module (-165 dBm) Add 3m 2D satellite positioning accuracy to any embedded system Low power consumption Up to 10Hz update rate NMEA (default) and RTCM protocols available Small PCB size for flexible designs 2.0 in × 0.8 in (5.0 cm × 2.0 cm) 6-pin Pmod port with UART interface Library and example code available in resource center The PmodGPS. 1 Functional Description The PmodGPS uses a standard 6-pin port and communicates via a 2-wire Universal Asynchronous Receiver/Transmitter (UART.) The PmodGPS also has a 2-pin port for control of the NRST pin to the module and the Radio Technical Commission for Maritime services, or RTCM pin for Differential Global Positioning System (DGPS) data using RTCM protocols. Note: The PmodGPS arrives with the RTCM feature inactive, to enable RTCM capabilities users should contact GlobalTop at: www.gtop-tech.com. DOC#: 502-237 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 1 of 6 PmodGPS™ Reference Manual 2 Interfacing with the Pmod The PmodGPS uses UART protocol for data transmission and reception. The interface operates at a default baud rate of 9.6 kBd, 8 data bits, no parity, and with single stop bits. However, users can change the baud rate to predefined values that range from 4.8 kBd to 115.2 kBd. The reset pin (NRST) on J2 allows normal operation in active low. If users toggle the NRST pin it will completely reset the module. This reset performs similar to a power cycling of the device. The 1 PPS pin on J1 provides a one pulseper-second output synchronized with GPS time (see the timing diagram in Fig. 1). The 3DF pin on J1 indicates the status of the user’s positional fix. When the module has a constant fix (2D or 3D) this pin stays low, if the module is unable to get a fix then the pin will toggle every second. (See Fig. 2) LD1 also follows this same behavior pattern in order to give the user a visual representation. Figure 1. 1PPS Pin Timing Diagram. Figure 2. 3DF Pin output without a fix. The PmodGPS also comes equipped with a coin cell retainer for a 12.5 mm coin cell battery. Users can significantly reduce the amount of time that it takes to acquire the first positional fix by installing a 3V coin cell battery. With the battery installed the module can also perform a hot start or a warm start instead of cold starting where users have to supply power to the VCC. Note: The ground square solder pad of the coin cell retainer may develop an oxide build up that will keep the battery from making a good connection. Users should simply scuff up the square solder pad inside J3 to remove any buildup. Oxide buildup may also occur if there has not been a battery in the retainer for a while. A cold start takes one or two minutes while outside in good conditions, and can take several minutes more if conditions are worse or the module is indoors. A hot start takes three to five seconds and a warm start varies depending on how long the module has sat unpowered. Users can hot start the PmodGPS only if it has acquired a fix within approximately the last two hours and with accessible backup power (coin cell battery) connected to the coin cell retainer. A warm start occurs when the battery is connected but the module has been without power for more than two hours. Users may utilize an external antenna at their discretion by installing a Linx Technologies Inc. CONSMA 003.062 module on header J4. The antenna can speed up acquisition of GPS signal in some conditions, especially if the antenna is outdoors and the module is indoors. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 2 of 6 PmodGPS™ Reference Manual The PmodGPS uses sentences based on National Marine Electronics Association (NMEA) protocols for data output. Each NMEA message begins with a ($) dollar sign. The next five characters are the talker ID and the arrival alarm. The PmodGPS talker ID is “GP” and the arrival alarm is the specific sentence output descriptor. Individual comma separated data fields follow these five characters. After the data fields there is an asterisk followed by a checksum. Each sentence should end with . For example output sentences refer to tables two through six at the end of this manual. User may configure some of the PmodGPS characteristics by writing command packets to the module. However, these functions are more advanced and not all of the command packets are openly distributed. Users may change the baud rate to 38.4kBd (minimum baud for 10Hz data acquisition) by issuing the following command over the UART: “$PMTK251,38400*27” The “*27” corresponds to a checksum, if users want to substitute a different baud rate, then they must calculate a new checksum using GlobalTop’s Checksum Tool. The command for changing the data acquisition from 1Hz to 10Hz is: “$PMTK226,3,30*4” The same checksum process for changing the baud rate applies to this change too. Contact GlobalTop for more information on the individual command packets, their complete command list, or see their FAQ for how to change the baud rate. Any external power applied to the PmodGPS must be within 2.7V and 5.25V; however, it is recommended that Pmod is operated at 3.3V. Pin 1 2 3 4 5 6 Signal 3DF RX TX 1PPS GND VCC Pin 1 Signal ~RST 2 RTCM Connector J1 Description 3D-Fix Indicator Receive Transmit 1 Pulse Per Second Power Supply Ground Power Supply (3.3v) Connector J2 Description Reset (active low) DGPS data pin (contact GlobalTop for use) Table 1. Interface connector signal descriptions. Note: Refer to the GlobalTop FGPMMOPA6H datasheet at here for more information on the GPS module interface. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 3 of 6 PmodGPS™ Reference Manual 3 Output Sentences Example $GPGGA 064951.000 2307.1256 N 12016.4438 E 1 8 0.95 39.9 M 17.8 M *65 Description Message ID UTC Time (hhmmss.sss) Latitude (ddmm.mmmm) N/S indicator Longitude (dddmm.mmmm) E/W indicator Position Fix Indicator Satellites used HDOP MSL Altitude Units Geoidal Separation Units Age of Diff. Corr. Checksum End of message indicator Table 2. GGA. $GPGGA,064951.000,2307.1256,N,12016.4438,E,1,8,0.95,39.9,M,17.8,M,,*65 Example $GPGSA A 3 29 21 …. 2.32 0.95 2.11 *00 Description Message ID Mode1 (see GlobalTop manual) Mode2 (see GlobalTop manual) Satellite used (CH1) Satellite used (CH2) Satellite Used (Ch12) PDOP HDOP VDOP Checksum End of message indicator Table 3. GSA. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 4 of 6 PmodGPS™ Reference Manual $GPGSA,A,3,29,21,26,15,18,09,06,10,,,,, 2.32,0.95,2.11*00 Example $GPGSV 3 1 09 29 36 029 42 …. 15 21 321 39 *7D Description Message ID Number of Messages Message Number Satellites in View Satellite ID (CH1) Elevation (CH1) Azimuth (CH1) SNR (C/No) Satellite ID CH(4) Elevation (CH4) Azimuth (CH4) SNR (C/No) Checksum End of message indicator Table 4. GSV. $GPGSV,3,1,09,29,36,029,42,21,46,314,43, 26,44,020,43,15,21,321,39*7D Example $GPRMC 064951.000 A 2307.1256 N 12016.4438 E 0.03 165.48 260406 3.05 W A *55 Description Message ID UTC Time (hhmmss.sss) Status (A = data valid) Latitude (ddmm.mmmm) N/S indicator Longitude (dddmm.mmmm) E/W indicator Speed over ground (knots) Course over ground (degrees) Date (ddmmyy) Magnetic Variation (degrees) E/W indicator Mode (see GlobalTop manual) Checksum End of message indicator Table 5. RMC. $GPRMC,064951.000,A,2307.1256,N,12016.4438,E,0.03,165.48,260406,3.05,W,A*55 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 5 of 6 PmodGPS™ Reference Manual Example $GPVTG 165.48 T Description Message ID Course (degrees) Reference (true or false) Course (degrees) Reference (Magnetic) Speed Units (N = knots) Speed Units (K = km/hr) Mode (see GlobalTop manual) Checksum End of message indicator M 0.03 N 0.06 K A *37 Table 6. VTG. $GPVTG,165.48,T,,M,0.03,N,0.06,K,A*37 4 Physical Dimensions The pins on the pin header are spaced 100 mil apart. The PCB is 2.0 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 6 of 6