由STM32F103C8T6和ISD1820，LCD1602，按键模块组成的录音设备，写一下ISD1820这一部分代码，并做出具体的解释，

ISD1820是一款语音录放模块，它可以通过模拟输入控制语音的录制、播放、停止等功能。下面是一个简单的示例代码：

#include <reg52.h>

#define KEY P1

sbit REC = P2^0;
sbit PLAY = P2^1;
sbit DELAY = P2^2;
sbit LED = P2^3;

void delay(unsigned int i)
{
    while(i--);
}

void write_cmd(unsigned char cmd)
{
    P3 = cmd;
    KEY = 0x02;
    delay(100);
    KEY = 0x00;
}

void write_data(unsigned char dat)
{
    P3 = dat;
    KEY = 0x03;
    delay(100);
    KEY = 0x01;
}

void init_lcd()
{
    write_cmd(0x38);
    write_cmd(0x0c);
    write_cmd(0x06);
    write_cmd(0x01);
}

void display_string(unsigned char x, unsigned char y, unsigned char *s)
{
    unsigned char i;
    if(x > 15 || y > 1) return;
    if(y == 0) y = 0x80;
    else y = 0xc0;
    y += x;
    write_cmd(y);
    i = 0;
    while(s[i] != '\0')
    {
        write_data(s[i]);
        i++;
    }
}

void main()
{
    REC = 1;
    PLAY = 1;
    DELAY = 1;
    LED = 0;

    init_lcd();
    display_string(0, 0, "Recording...");

    while(1)
    {
        if(REC == 0)
        {
            LED = 1;
            display_string(0, 1, "Recording...");
            write_cmd(0x01);
            write_cmd(0x80);
            write_data('R');
            write_data('E');
            write_data('C');
            write_data('O');
            write_data('R');
            write_data('D');
            write_data('I');
            write_data('N');
            write_data('G');
            delay(1000);
            LED = 0;
            display_string(0, 1, "Record done.");
            write_cmd(0x01);
            write_cmd(0x80);
            write_data('R');
            write_data('E');
            write_data('C');
            write_data('O');
            write_data('R');
            write_data('D');
            write_data(' ');
            write_data('D');
            write_data('O');
            write_data('N');
            write_data('E');
            delay(1000);
            write_cmd(0x01);
        }
        if(PLAY == 0)
        {
            LED = 1;
            display_string(0, 1, "Playing...");
            write_cmd(0x01);
            write_cmd(0x80);
            write_data('P');
            write_data('L');
            write_data('A');
            write_data('Y');
            write_data('I');
            write_data('N');
            write_data('G');
            delay(1000);
            LED = 0;
            display_string(0, 1, "Play done.");
            write_cmd(0x01);
            write_cmd(0x80);
            write_data('P');
            write_data('L');
            write_data('A');
            write_data('Y');
            write_data(' ');
            write_data('D');
            write_data('O');
            write_data('N');
            write_data('E');
            delay(1000);
            write_cmd(0x01);
        }
        if(DELAY == 0)
        {
            LED = 1;
            display_string(0, 1, "Delaying...");
            write_cmd(0x01);
            write_cmd(0x80);
            write_data('D');
            write_data('E');
            write_data('L');
            write_data('A');
            write_data('Y');
            write_data('I');
            write_data('N');
            write_data('G');
            delay(1000);
            LED = 0;
            display_string(0, 1, "Delay done.");
            write_cmd(0x01);
            write_cmd(0x80);
            write_data('D');
            write_data('E');
            write_data('L');
            write_data('A');
            write_data('Y');
            write_data(' ');
            write_data('D');
            write_data('O');
            write_data('N');
            write_data('E');
            delay(1000);
            write_cmd(0x01);
        }
    }
}

上述代码中，我们使用了LCD1602显示模块来显示当前录音状态，按键模块来控制录音、播放和延时功能。

在录音功能中，我们通过判断REC按键是否按下，来进入录音状态，并通过LED指示灯和LCD1602模块显示当前状态。在录音完成后，同样通过LED指示灯和LCD1602模块显示录音完成。

在播放和延时功能中，同样通过判断PLAY和DELAY按键是否按下，来进入播放和延时状态，并通过LED指示灯和LCD1602模块显示当前状态。在播放或延时完成后，同样通过LED指示灯和LCD1602模块显示操作完成。

ISD1820模块的控制部分，需要使用模拟输入方式控制其录制、播放、停止等功能，我们在代码中并未给出具体的ISD1820模块控制代码。如果需要使用ISD1820模块，可以参考其官方文档或者第三方资料。