Design of Embedded MP3 Player Module Based on BU9435

1 Introduction

MP3 is not only small in size, light in weight, large in storage capacity and low in power consumption. And MP3 does not require any mechanical movement to access the storage medium. Therefore, MP3 also has strong anti-vibration capability without any mechanical noise advantages. With the increasing capacity of flash memory and the continuous price reduction, MP3 is in the field of car and portable audio. More and more people are welcome, especially in the field of portable audio, MP3 has occupied an absolute mainstream position.

SD card is a highly versatile storage medium widely used in digital cameras, mobile phones and portable media players: U disk is the most common mobile storage device, it is easy to use, security and convenience. The aspect is much better than other mobile storage products. ROHM has developed the LSI-BU9435 that integrates the USB storage/SD card host (HOST) function, MP3 audio decoding function, and system control functions. The BU9435 supports both USB flash drives and SD cards as storage media, making it ideal for small stereos, car stereos and portable media playback devices. With BU9435 as the core, design an MP3 player module. The module can be easily embedded into a variety of audio equipment to provide a rich medium for audio equipment.

2 Introduction to BU9435

The BU9435 not only integrates the system controller and MP3 audio decoder, but also has built-in USB storage/SD card host function, which can automatically find MP3 files in U disk and SD card, and play high-quality music comparable to CD through decoder. . Previously, an MP3 decoding solution with a USB host interface required an external program memory or a CPU, a USB controller, and an MP3 decoder. Now only BU9435 is required.

Main features of BU9435: USB full-speed HOST interface, SD memory card interface; MP3 decoder with ID3Tag analysis function for displaying file/folder number, playback time, artist name, title, etc.; system controller with built-in command software ;FATl6/FAT32 file system; independent work/slave work mode conversion function; I2C bus interface; 4×3 matrix keyboard scan control function; 7-channel LED control function; automatic sampling rate conversion function; multiple equalization modes. Figure 1 shows the internal block diagram of the BU9435.

Main pin functions of BU9435: pin 1 (RESETX): reset terminal, active low; pin 2 (SEL_SLAVE): operating mode selection, high level select independent operating mode, low level is slave mode; pin 3 (SEL_MP3): file format selection, high level only supports MP3 format files, low level supports MPl, MP2 and MP3 format files; pin 4 (SEL_DOUT): audio output selection, high level for analog audio output Low level is digital audio output; pin 5 (SEL_VOL): volume control selection, high level enable volume control function, low level disable volume control; pin 6 (SEL_APLAY): auto play selection terminal, high power It is forbidden to play automatically, low level selects auto play; Pin 10~13: When working in standalone mode, 10~13 pins are matrix keyboard line input terminal KEY_ROWn; when working in slave mode, 10 pins are track switching output At the end, when the MP3 track is switched, the output is low, and the 11 pin is the BU9435 busy flag output. 12 to 13 pins are SCL and SDA for I2C bus: Pins 14 to 16: When operating in standalone mode, 14 to 16 pins are matrix keyboard column output KEY_COLn; when operating in slave mode, 14 pins and 15 leads The pin is the I2C bus low address select terminal A0 and Al, the 16 pin is the slave mode select terminal, the high level select mode 2, the low level select mode 3; pins 19 to 23: SD card interface; pin 33 (USB_DM) And pin 34 (USB_DP): USB interface; pin 40 (XIN_PLL) and pin 4l (XOUT_PLL): clock generation circuit, external 16.934 4 MHz crystal oscillator; pin 44 (RDACO) and pin 46 (LDAC0): analog audio right channel and left channel output; pin 48 (AMUTE): mute state output, low level means muted; pins 49 to 55: when operating in standalone mode, 49 to 55 The pin is the working status LED indicating the output: when operating in the slave mode, the 53 to 55 pins are digital audio outputs.

3 BU9435 peripheral circuit design

The schematic diagram of the MP3 decoding circuit composed of BU9435 is shown in Fig. 2. In order for the BU9435 to work as intended, its pins must be configured accordingly. Most of the input pins have a pull-up function inside. The main configuration is: 2-pin grounding, so that the BU9435 operates in the slave mode, so that the system controller can control the BU9435 through the I2C bus and obtain the working status of the BU9435: 3 The grounding of the foot, the system supports MPl, MP2, MP3 format files; 4 pins are left floating, the internal pull-up is high level, the device output is analog audio signal; there are usually other audio sources in the system. Generally, there are independent channel selection and volume control devices, so the BU9435 5 pin is grounded to disable the device volume control: 6 pins are left floating, the device is prohibited from playing automatically, and the main controller controls BU9435; the highest address of the I2C device of BU9435 is fixed at 1, the lowest 2 bits are determined by pin 14 and pin 15, the other bits are 0, pin 14 and pin 15 are grounded, and the I2C device address of BU9435 is 0x80H.

The stereo analog audio signal is output by pin 44 and pin 46 and is RE filtered to the volume control device control channel and volume. Control of the BU9435 and acquisition of the state of the BU9435 are all done by the I2C bus pins SCL and SDA.

4 software design

Control BU9435 first sends a control command, and then reads the status register group of BU9435 or the corresponding information. The length of the control command is 2 to 8 bytes, depending on the command. The related information of the playback, such as BU9435 internal status, folder information, playback time information and ID3Tag information, are read out through the I2C bus. It should be noted that when reading BU9435, the first byte returned by BU9435 is not the valid content of the status register group or the corresponding information, but a dummy byte that reflects whether the subsequent content is valid. If the byte is 0x00H. It indicates that the subsequent content is a valid status register group or corresponding information data; if the byte is 0xFFH, it indicates that BU9435 is busy, and subsequent data is invalid. At this time, the main controller should send an I2C end command and re-read. Figure 3 is a flow chart for reading BU9435.

When the BU9435 is working in different states, the commands received are different. When a command cannot be received by the current state, the command will be ignored. The relationship between the state of BU9435 and the main command is shown in Table 1. The BU9435 system control software flow is shown in Figure 4.

5 Conclusion

The MP3 player module based on BU9435 not only supports U disk and SD card as storage medium at the same time, but also provides rich media for the sound system, and the peripheral and interface circuits are simple. As long as the system provides I2C bus interface, the module can be easily embedded into the module. In the system, there is strong versatility. The MP3 player module can provide useful reference and reference for both the design of the new sound system and the upgrade of the old sound system.

references:

[1]. MP2 datasheet http://

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