Global Positioning System (Global Positioning System, GPS ) is a non-autonomous navigation and positioning system developed by the United States since the 1970s and fully completed in 1994. It is based on receiving navigation satellite signals. His ability to provide high-precision 3D position, 3D speed and time information with global coverage, all-weather, and continuous real-time capabilities has solved human navigation and positioning issues. With the continuous improvement of the global positioning system, the continuous improvement of hardware and software, the application field is constantly being developed, and it has been widely used and developed in both military and civilian fields. In practical applications, after receiving the signal of the orbiting satellite, the GPS receiver demodulates and outputs the GPS positioning data in a standard format. This data must be further processed before it can be displayed on the user data terminal. 1 GPS receiver output data format NMEA-0183 is a general interface standard developed by the National Marine Electronics Association for asynchronous communication of nautical instrument data. It is a string of ASCII characters. The GPS receiver outputs GPS positioning data in the NMEA-0183 standard format. The data terminal equipment needs to obtain position information and time information from the NMEA0183 data stream output by the GPS in real time. The GPS receiver provides multiple sentence formats, including GPGGA, GPGSA, GPGSV, GPRMC, GPZDA and GPGLL. The user can select one or more sentence output as needed. The system chooses to receive and parse GPGLL and GPZDA to obtain geographic location information and UTC time information (including date), respectively. UTC time is corrected by time difference to obtain local time information. The NMEA0183 statement contains multiple data items, separated by commas, and the statement ends with a carriage return (CR) and line feed (LF) character. The GPZDA statement format is as follows: In the above statement, the meaning of each data item is as follows: ①Statement type: $ GPZDA; ② UTC time: 14523.62; ③ UTC day: 01 ～ 31; ④ UTC month: 01 ～ 12; ⑤ UTC: year 2001; ⑥ local time difference: 10 hours; ⑦ local time difference: 34 points; ⑧ checksum: 6E. The checksum includes the $ character. The GPGLL statement format is as follows: In the above statement, the meaning of each data item is as follows: ①Sentence type: $ GPGLL; ② Latitude value; ③ North latitude; ④ Longitude value; ⑤ West longitude; ⑥ UTC time, hour, minute, minute, second, second. Seconds seconds format; ⑦ state, A = positioning, V = not positioning; ⑧ checksum: 2C. The checksum includes the $ character. Receiving the above GPS information is done by the UART of AT89C2051 microcontroller. GPGLL is 55 characters and GPZDA is 38 characters. Considering the limited internal RAM unit of the single-chip microcomputer, in order to adapt to the situation that the GPS simultaneously outputs more data patterns and a larger amount of data, it is necessary to selectively receive the pattern.
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