1 GSM-R handheld terminal function overview
The Ministry of Railways has determined to use the GSM-R system as the wireless communication platform for China's railways. Therefore, it is imminent to establish a comprehensive wireless communication system based on the GSM-R platform to provide wireless communication means and equipment for various operations of the GSM-R network.
The response speed of WT588D receiver is relatively fast. The time from triggering to broadcasting and sending BUSY feedback signal is less than 5ms, which can cater to the speed pursued by the whole system. In terms of supporting software, from voice editing to downloading voice engineering, the operation tends to be a simple mode, which is not only well used by senior designers, but also suitable for beginners to do experimental tests.
GSM-R handheld terminals have special applications in marshalling stations. The operation of the marshalling station takes the group as a unit to complete the shunting and marshalling work. Each member of the team is equipped with a GSM-R professional handheld terminal, and has its own functions according to different job requirements. This article mainly introduces the implementation of the voice feedback function. The types of scheduling commands issued by the shunter are limited. Therefore, the GSM-R handheld terminal can pre-store the voice information of the corresponding command, and then play the corresponding voice according to the received scheduling command. This function is a must-have function for handheld terminals of marshalling stations. This article uses ATMEGA48 and WT588D voice chips to complete this function, and uses a new method to efficiently complete the communication and control between ATMEGA48 and WT588D voice chips, fully playing ATMEGA48 high-speed Features.
2 Device Brief
This article uses the SPI control interface between the WT588D voice chip and ATMEGA48 to complete the required voice feedback function.
ATMEGA48 is a model of AVR single chip microcomputer. The AVR core has a rich instruction set and 32 general working registers. All registers are directly connected to the arithmetic logic unit (ALU), so that an instruction can simultaneously access two independent registers in a clock cycle. It also abolishes the machine cycle, uses a streamlined instruction set, uses words as the unit of instruction length, arranges the rich operands and opcodes in one word, the instruction fetch cycle is short, and instructions can be prefetched to achieve pipeline operations. Can execute instructions at high speed. This structure greatly improves code efficiency, and has a data throughput rate up to 10 times that of ordinary CISC microcontrollers. It has achieved optimized balance in many aspects such as software / hardware overhead, speed, performance and cost, and is a cost-effective single-chip microcomputer.
WT588D voice chip adopts the technology that voice data is directly stored in SPI-Flash memory, with fast download speed and output after D / A conversion. Therefore, speech, music, tones and sound effects can be reproduced very realistically and naturally. Multi-function, good sound quality, wide application range and stable performance are the special features of the WT588D series of voice chips, which make up for the shortcomings of the past narrow application fields of various types of voice chips. Can completely replace ISD1700, ISD1425, ISD4000, PM50 and other voice chips.
The WT588D series voice chip has the following characteristics: simple voice content change, convenient playback; high sound quality, natural sound; support 2M ~ 64M SPI-Flash memory, can achieve 2149S playback under 6K sampling; manual operation / microcontroller Control compatible; edge trigger or level trigger can be used during playback; loop playback can be performed; with automatic power-saving control, the quiescent current is less than 10uA during power-saving; information storage does not require a back power supply; up to 220 voices can be loaded; PWM output can be Directly push 0.5W / 8Ω speaker; can be repeatedly erased and programmed 100,000 times; playback can be controlled by single chip programming; single power supply operation; module package (with FLASH memory) is 16-pin and 28-pin embedded, chip package is DIP18 , SSOP20 and LQFP32 formats.
WT588D VoiceChip software is the corresponding supporting software developed according to the characteristics of WT588D voice chip. It completes the writing of various control mode programs of the WT588D voice chip very well. When the MCU port line is not enough, one-line serial port control or SPI serial port control can be selected. It is used in the occasion of single chip microcomputer. The software can also complete voice replacement, combination, audio output mode setting, etc., and the operation interface is simple and the editing process is convenient.
3 hardware circuit design
All operations of WT588D are controlled by the microcontroller, and the operation commands can be sent through the serial communication interface SPI. The SPI protocol assumes that the SPI shift register of the microcontroller acts on the falling edge of SCLK, so for the WT588D, the data on the MOSI pin is latched on the rising edge of the clock. The ATMEGA48 SPI interface is used to directly control the WT588D, so the hardware design is relatively simple. As shown in Figure 1.
ATMEGA48 as SPI master device, WT588D as SPI slave device. ATMEGA48 selects WT588D through the / SS chip, and the MOSI control line sends control information to WT588D to play the corresponding voice information. When the WT588D reads the end of the voice, an interrupt will be generated. ATMEGA48 receives this interrupt and plays the next segment of voice.
The specific pin connections are as follows:
1. The SS of ATMEGA48 is connected to the CS of WT588D. When ATMEGA48 operates the WT588D, the chip is selected.
2. The MOSI of ATMEGA48 is connected to the DATA of WT588D for data transmission.
3. The SCLK of ATMEGA48 is connected to the CLK of WT588D to provide a clock for serial data.
4. The interrupt line of ATMEGA48 is connected to the BUSY of WT588D, which can be used as an interrupt signal for the completion of voice playback.
5. WT588D can be set to DAC (external power amplifier) ​​output or PWM (direct drive speaker) output to play the selected voice information.
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