Implementation of Universal GSM Wireless Fax Terminal Based on W77E58 Microcontroller(1)

Single chip microcomputer STM32L151CCU6

Crystal oscillator

Mobile phone crystal 3.2*2.5mm 3225 26M (26.000MHZ) 7.5PF 10PPM 20PPM 30PPM

1 Introduction

With the continuous advancement of the modern information society, wireless technology and GSM network have also developed rapidly. As a new business of GSM, wireless fax has outstanding features such as real transmission and real-time recording, especially suitable for news interviews and traffic. In the fields of transportation, mobile office, public security and anti-drug, it can maximize the advantages of wireless communication, so that users can truly have their own "mobile office." This paper elaborates on the hardware and software implementation of a universal GSM wireless fax terminal equipment. The device can be used as a peripheral terminal for other client systems to send and receive command and fax data.

2 hardware implementation of wireless fax terminal

The wireless fax terminal equipment we designed uses Taiwan's Winbond's 8-bit single-chip W77E58 as the main control module. The external wireless GSM/GPRS module Q2403A and other peripheral circuits of WAVECOM Company form a universal GSM wireless fax terminal.

● The MCU of the main control module uses Winbond's eight-bit machine W77E58. The W77E58 is a multi-programmable fast microprocessor compatible with the MCS51 series of microcontrollers. It integrates 32KB of reprogrammable Flash ROM, 256-byte chip memory, and SRAM for IKB access with MOVX instructions. Program watchdog timer, three 16-bit timers, two enhanced full-duplex serial ports, on-chip RC oscillator, dual 16-bit data pointers, and more. In many cases, the system requirements can be met with almost no expansion of the peripheral chip. Because it uses a newly designed microprocessor core to remove redundant clock and storage cycles, at the same crystal frequency, depending on the type of instruction, its operating speed is generally 1.5 to 3 times faster than the traditional 8051 series. Under normal circumstances, the average can reach more than 2.5 times. In addition, because the W77E58 uses a fully static CMOS design, it can operate at low speed crystal frequencies. Compared with the ordinary 8051, if the W77E58 uses a low-speed operating frequency, the power-saving performance of the W77E58 will be greatly improved under the same command throughput.

The main functions of the main control module are:

1 The main control module initializes the GSM wireless module through the AT command, and establishes a connection with the GSM network through the GSM module, thereby establishing a connection with the target fax terminal, and coordinating the hardware components to complete the transmission and reception of the fax proof.

2 The main control module sends and receives data or instructions to the client system through the RS232 serial port;

3 The main control module takes autonomous operation or takes other operations according to the remote control command.

● The GSM wireless module uses the Q2403A module of WAVECOM. The Q2403A module consists primarily of an RF antenna, internal Flash, SRAM, GSM baseband processor, matching power supply and a 60-pin socket. The GSM baseband processor is the core component that handles AT commands sent by external systems through the serial port. The RF antenna section mainly implements signal modulation and demodulation, as well as signal conversion between the external RF signal and the internal baseband processor. The matching power supply provides the required power to the processor and RF section. The Q2403A module supports GSM900 and GSMl800 dual-band networks with a receiving rate of 26.8 kbits/s and a transmission rate of 13.4 kbits/s, supporting AT FAX class2 fax communication procedures.

The GSM wireless module acts as the wireless transceiver module of the fax terminal. The main function is to establish a communication bridge between the main control module and the GSM network, so that the AT command can be transmitted between the main control module and the target fax terminal, and the connection is established. The fax data of the main control module is modulated and sent to the destination fax machine, or the fax data sent by the target fax machine is demodulated and sent to the main control module, thereby completing the transmission and reception of the entire fax proof.

In addition, the Q2403A can expand a lot of interfaces, SIM card interface, I / O interface, parallel LCD interface, keyboard, microphone input and headphone output. The SIM card must be externally connected. The user must also install a SIM card that has registered a wireless fax service with the GSM network operator to complete the wireless fax communication.