Clock information display system based on single chip microcomputer and GPS

GPS (global positioning system) is a system that uses information transmitted by 24 GPS earth satellites in the United States to provide positioning, navigation, timing and other services. Since the GPS system was opened to the world for free in 1993, it has been widely used in various industries around the world. The GPS system is widely used in navigation, geodesy, precise timing, vehicle positioning and anti-theft. This article introduces the design method of using the GPS-OEM receiving board GN-77N and AT89C52 microcontroller of Japan's Furuno Company to realize the reception and display of clock information.

1 System Hardware Interface

GN-77N is a GPS-OEM receiver board launched by Furuno Corporation of Japan. This receiver board is a parallel 8-channel receiver that can track 8 satellites at the same time. It has powerful functions such as high-precision timing, fast positioning speed, ultra-low power consumption, ultra-small size, pin-type installation, and super anti-electromagnetic interference ability. It provides users with the best solution in various applications.

1.1 GN-77N Pin Function

The pin functions and descriptions of the receiving board are shown in Table 1.

Table 1 Pin functions and descriptions of the GN-77N receiver board

1.2 AT89C52 MCU and GPS clock information display system hardware circuit

The system uses AT89C52 single-chip microcomputer, 12MHZ crystal oscillator, serial port mode 1 to receive GPS information, P1 port and P2 port and 74LS138 as 6-bit seven-segment common anode LED display interface, which can display real-time time and other GPS information data in turn. The system hardware circuit connection diagram is shown in Figure 1.

Figure 1 System hardware circuit connection diagram

2 System software interface

2.1 GN-77N module data format

In this design, the communication baud rate of GN-77N is set to 4800, 1 start bit, 8 data bits, 1 stop bit, and no parity check. The NMEA-0183 format output of serial port 1 is used. NMEA-0183 is a standard format developed by the American Marine Electronics Association for marine electronic equipment. The data code is ASCII code characters, and the format transmitted in the GPGGA sentence is:

$GPGGA,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M,<10>,M,<11>,<12>*hh where

$GPGGA is the start character and statement format description (this sentence is GPS positioning data), <1> is UTC time, in the format of hours, minutes, seconds.

For example: $GPGGA,104530,3105.3535,N,12207.1258,E,1,03,13.8,46.5,M,12.3,M,,*4A means that the UTC time is 10 hours 45 minutes 30 seconds, the position is 31 degrees 5.3535 minutes north latitude, 122 degrees 7.1258 minutes east longitude, ordinary GPS positioning method, 3 satellites are received, the horizontal accuracy is 13.8 meters, the antenna height is 46.5 meters above sea level, the location height is 12.3 meters above ground level, and the checksum is 4AH.

2.2 Software design of clock information display system

The system program includes the main program, data receiving subprogram, time conversion subprogram and display subprogram. Assume that the received time information is placed in the display buffer. The address of the display buffer is 60H, 61H, ..., 65H, which stores the hours, minutes, and seconds in sequence. The program is as follows:

ORG 0000H

LJMP MAIN

ORG 0030H

MAIN: MOV PSW,#00H

MOV PCON,#80H; double the baud rate 2400×2＝4800BPS

MOV SCON,#50H ; Set to serial port 1 mode

MOV TMOD,#20H; T1 works in mode 2

MOV TH1,#0F4H ; Set the initial value to 2400BPS

MOV TL1,#0F4H ; Set the initial value to 2400BPS

SETB TR1 ; Start timer T1

CLR ES

CLR TI

CLR RI

LOOP: JNB RI,$

LCALL INT

LJMP LOOP

INT: LCALL INT1

LCALL RECEIVE

LCALL SETDATA

LCALL DISP

RET

INT1: LCALL SS; judge $GPGGA

XRL A,#24H

JZ INT2

LJMP INT1

INT2: LCALL SS

XRL A,#47H

JZ INT3

LJMP INT1

INT3: LCALL SS

XRL A,#50H

JZ INT4

LJMP INT1

INT4: LCALL SS

XRL A,#47H

JZ INT5

LJMP INT1

INT5: LCALL SS

XRL A,#47H

JZ INT6

LJMP INT1

INT6: LCALL SS

XRL A,#41H

JZ INT7

LJMP INT1

INT7: LCALL SS

RET

RECEIVE: LCALL SS; Time received, hours, minutes, seconds

MOV 60H,A

LCALL SS

MOV 61H,A

LCALL SS

MOV 62H,A

LCALL SS

MOV 63H,A

LCALL SS

MOV 64H,A

LCALL SS

MOV 65H,A

RET

SS: JBC RI, SS1

LJMP SS

SS1: MOV A,SBUF

RET

SETDATA: MOV A,60H ; Time conversion subroutine

…

SETH: MOV A,60H

…

ADD A,#8 ;Convert UTC time to Beijing time

MOV B,A ; if the time is greater than 24, subtract 24

SUBB A,#24

JC SETH1

LJMP SETH2

SETH1: MOV A,B

SETH2: MOV B,#10

DIV AB

ADD A,#30H ;Convert the processed characters into ASCII code

…

RET

DISP: MOV R0, #60H; Display subroutine

…

RET

3 Conclusion

Due to the development of computer technology, network technology, communication technology, GPS positioning technology and other related technologies, as well as the characteristics of all-weather, high-precision and automatic measurement of GPS technology, as an advanced measurement method and new productivity, it has been integrated into various application fields of national economic construction, national defense construction and social development. Therefore, the research and application of GPS system will greatly improve productivity and generate huge economic benefits. The clock information display system based on single-chip microcomputer and GPS introduced in this article can obtain accurate time and positioning information, provide convenience for people's daily life, and avoid the inconvenience caused by inaccurate clock. At the same time, it also opens up a better use for the application of GPS system, which has broad practical significance.

The innovation of this paper is that the accuracy of the time signal is directly related to people's daily life, industrial production and social development. The clock information display system based on single-chip microcomputer and GPS introduced in this paper can not only obtain accurate time information from the GPS navigation system, but also has the characteristics of simple hardware circuit, low cost, convenient programming and stable performance, which has certain use value. In addition, the reception and processing of latitude, longitude and other GPS information data can be realized by simply adding corresponding subroutines in the software part.

References:

[1] Wang Huinan, GPS Navigation Principles and Applications. Beijing: Science Press, 2003

[2] He Limin, Single Chip Microcomputer Application System Design. Beijing: Beijing University of Aeronautics and Astronautics Press. 1993

[3] Li Guangfei, Single-chip microcomputer control and display system of GPS positioning information, Microcomputer Information (Measurement and Control Automation), Vol. 20, No. 11, 2004

[4] Li Duo, Development of high-precision system clock using GPS receiving board, Microcomputer Information, Vol. 15, No. 4, 1999

[5] Liu Xiao et al., Design of GPS data collection system based on single chip microcomputer, Journal of Qingdao University of Science and Technology, 2006.02