Design and implementation of GPRS data transmission module

1 Introduction

With the increasing demand for wireless data services in the market, operators have vigorously developed data services in their own fields, striving to gain an advantage in the fierce competition. The traditional GSM network can only support data transmission services at a rate of 9.6 kb/s, which is far from meeting the needs of users for high-speed wireless data services. General Packet Radio Service (GPRS) is a standardized packet switching data service built on the traditional GSM network. It can provide packet data services at a rate of up to 115 kb/s, making the transmission of multimedia services including pictures, voice and video in wireless networks a reality.

GPRS is considered an important step in the evolution of the second generation mobile communication system to the third generation mobile communication. Compared with the original GSM dial-up circuit switching data transmission method, GPRS is a packet switching technology with the advantages of "high speed" and "always online". GPRS allows users to send and receive data in an end-to-end packet transfer mode without using the network resources of the circuit switching mode, thus providing an efficient and low-cost wireless packet data service. With the rapid development of wireless data transmission technology, GPRS has become the best bearer for wireless data services.

2 Hardware Design

2.1 Siemens MC55 module

The GPRS module selected for this study is the Siemens MC55 module, which is the smallest tri-band module on the market today. The end-to-end connector of the MC55 is connected to the chip application platform via a 50-pin 0.5 mm wide pin. The 50 pins are used to control the various logic units, transmit data and audio signals, and supply power supply queues. A versatile audio concept provides a variety of audio interfaces, each of which can be used on the end-to-end connector: 1 digital audio interface (DAI) and 2 analog audio interfaces. Using AT commands, you can easily connect back and forth and select commands for different audio modes.

The most important states of MC55 are 0 V (for low data bits and ON state) and 2.65 V (for high data bits and OFF state). This chip is designed to be used as a data communication equipment (DCE). Based on the traditional DCE-DTE connection, it communicates with the user application end via serial port. The serial interface is shown in Figure 1.

2.2 GPRS data transmission module hardware design

This research design mainly uses GPRS module and single-chip microcomputer for data transmission, so the hardware involved is mainly single-chip microcomputer and GPRS module. The GPRS module selected here is Siemens MC55, and the single-chip microcomputer is 51 series.

The data communication between the GPRS module and the microcontroller is mainly completed through data transmission between ports TXD0 and TXD, and between RXD0 and RXD. The TXD0 port on the GPRS module is used to receive data from the microcontroller, while the TXD port on the microcontroller is used to transmit data to the GPRS module. The RXD0 port on the GPRS module is used to send data to the microcontroller, while the RXD port of the microcontroller is used to receive data transmitted from the GPRS module.

Since the module has 5 power pins and the voltage is 3.3~4.8 V, the 5 pins are connected together and directly connected to the external power supply. The pin IGT on the GPRS module is mainly used for ignition reset. Here, it is used to make a reset conversion of the GPRS module. There is an integrated SIM interface on the baseband processor of MC55, which is directly wired to the host interface (end-to-end connector) for connecting to the external SIM card holder. The SIM card connected here has 6 pins CCCLK, CCVCC, CCIO, CCRST, CCIN and CCGND, which are connected to the 1st to 6th pins of MC55 respectively. The distance between the connector of the module and the pin of the SIM card holder should not exceed 20 cm. In order to achieve the best effect, a layer of copper isolation net is laid under the SIM bracket, and this layer of copper is connected to the CCGND pin of the SIM card. The two capacitors between CCVCC and CCGND should be as close to the pins as possible, and the wiring impedance should be as low as possible to meet the specification requirements. The microcontroller is connected to the keyboard, and data can be sent to the microcontroller through the keyboard. The crystal oscillator of the microcontroller is 11.0592 MHz, and the data transmission rate is set to 9600 b/s. The microcontroller is reset when the reset button RESET is high.

The circuit schematic diagram of the hardware part of the GPRS data transmission module is shown in Figure 2.

3 Software System

This program is mainly used to complete the data transmission between the GPRS module and the microcontroller. The microcontroller is a 51 series. The microcontroller serial port is set to work in mode 1, 8-bit UART, and the data transmission rate is variable; the working mode of timer 1 is mode 2, the data transmission rate is set to 9 600 b/s, and the crystal oscillator is 11.059 2 MHz. We mainly transmit AT commands, which include the dialed number, the IP address of the DNS service, the password of the GPRS service provider, and the APN for accessing the GPRS service. Of course, a TCP communication needs to be established. The customer content of this service includes the IP, address, and TCP port number of the remote host. The above is the information transmitted.

The main program of this program is to send and receive AT commands. When completing sending and receiving data, the data sending subroutine and data receiving subroutine are called respectively. There are three subroutines here: data sending subroutine, data receiving subroutine and delay subroutine.

The program flow chart is shown in Figure 3 and Figure 4.