ISD2500+ATmega8 realizes intelligent voice system

1 Introduction

With the rapid development of semiconductor technology and computer technology, voice technology is also making continuous breakthroughs, especially speech synthesis technology is becoming more and more perfect, and new voice chips are constantly emerging. The ISD2500 series voice chips produced by ISD of the United States can adopt single-chip control mode or microprocessor control mode.

2 Introduction to ISD2500 Series Voice Chip

The ISD2500 series voice chip is a high-fidelity recording and playback integrated single-chip solid-state voice integrated circuit. It uses ISD's patented "direct analog storage technology" to successfully store analog data in semiconductor memory. This breakthrough EEPROM storage method can write analog data directly into a single storage unit without the need for A/D or D/A conversion. The effects of this technology are: (1) increased integration compared to equivalent digital methods; (2) the storage of analog data is non-volatile. According to the different recording and playback times, the ISD2500 series chips can be divided into four models: ISD2560, 2575, 2590 and 25120.

2.1 ISD2500 Package and Pin Function

ISD2500 adopts DIP-28 package, the pin arrangement is shown in Figure 1, and the pin functions are listed in Table 1.

2.2 Working Mode

When the highest address bits (MSB) A8 and A9 are both high, the address terminal is used as the operation mode selection terminal (high level is valid). Its working mode is shown in Table 2.

There are two points to note when using the working mode:

(1) Operations in all working modes start from address 0. Subsequent operations start from the corresponding address according to the different modes. When the circuit is recording or playing back or entering the power saving state, the address counter is reset to 0.

(2) The working mode bit is not locked, and the working mode operation can be executed at any time when the MSB address bit is high and the CE level becomes low. If one (or two) of the MSB address bits becomes low in the next chip selection cycle, the information address is executed, that is, recording or playing from this address, and the originally set working mode state is lost. [page]

3 ISD2500 and MCU interface and programming

The ISD2500 series voice chip has a simple structure and is easy to use. It can form a simple single-chip application system. However, in many cases, since the recording/playback of voice data needs to be automatically controlled by other signals, the single-chip ISD2500 cannot meet the application requirements. At this time, it is necessary to use the voice system of the microcontroller to combine different working modes and flexibly record and play multiple messages as needed. ISD2500 can form an intelligent voice system with various microcontrollers. This article uses ATmega8 in Atmel's AVR series of microcontrollers as an example to form a basic circuit with ISD2500. This circuit is a hardware platform that can be expanded accordingly according to different requirements.

Taking the playback process as an example, the operation process is as follows:

(1) Power on the device;

(2) PD terminal is set to low level;

(3) Enter the playback start address;

(4) After waiting for the power-on delay (TPUD), the CE terminal changes from high to low, and the falling edge performs the playback operation. At this time, the device no longer affects the re-jump of the address terminal and the recording and playback control terminal. Note that the above pins should be kept stable within the control/address setup time (TSET) before CE changes low;

(5) When encountering the EOM mark, the device continues to output sound, and when the EOM pulse (TEOM) ends, the sound playback stops.

The recording operation is basically the same as the playback operation and will not be described in detail.

The specific hardware connection circuit is shown in Figure 2. Among them, S1 is the "record" key, S2 is the "play" key, and S3 is the "segment" operation key.

When using a single-chip microcomputer to control ISD2500, the following points should be noted:

(1) The address setup time (TSET) of the ISD2500 series is 300 ns, which means that the address signal should be delayed by 300 ns before the falling edge of CE. Some very fast microcontrollers need to add a delay.

(2) The typical value of the ISD2500 series EOM pulse width is 12.5 ms. When playing, you can use the query or external interrupt method to detect the rising edge of the EOM terminal, because only when the EOM terminal becomes a high level, the CE signal can start the next operation. The software flow is shown in Figure 3.

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4 Conclusion

The test proves that the ISD2500 series voice chip and ATmega8 MCU have achieved good results. It can be easily expanded and transplanted, and applied to robot voice prompts, aircraft automatic warning, ECG signal recording and playback systems, etc., and has a very broad application prospect.