410-237P Digilent

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. Copyright Digilent, Inc. All rights reserved. DOC : 502-237 Page 1 of 6 Other product and company names mentioned may be trademarks of their respective owners. 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 pulse- per-second output synchronized with GPS time (see the timing diagram in Fig. 1). The 3DF pin on J1 indicates the status of the users 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. Page 2 of 6 Other product and company names mentioned may be trademarks of their respective owners.