根据文档中提供的信息，完成文档中的要求，将所有.c和.h文件以及所有包含的需要的代码都写出来，尽可能简洁明了，但不要框架。矩阵按键按下后，矩阵扫描扫描到电平变化，蜂鸣器工作发出声音，电平变化结束蜂鸣器停止工作

为了实现您所描述的功能——即当矩阵按键被按下后，蜂鸣器会发出声音，并且数码管上会显示出相应的编号，我们需要对现有的代码进行扩展。以下是整合后的`main.c`及`main.h`文件的内容：

### main.h

#ifndef __MAIN_H__
#define __MAIN_H__

#include <STC32G.H>
#define MAIN_Fosc 12000000UL

typedef unsigned char u8;
typedef unsigned int u16;
typedef unsigned long int u32;

sbit DS = P2^0;
sbit ST = P2^1;
sbit SH = P2^2;
sbit COM1 = P0^0;
sbit COM2 = P0^1;
sbit COM3 = P0^2;
sbit BUZZER = P1^7;  // 蜂鸣器控制端口定义

u8 SEG_Code[13] = {0x3f, 0x06, 0x5b, 0x4f, 0x66, 0x6d, 0x7d, 0x07, 0x7f, 0x6f, 0x00, 0x40, 0xFF};

void delayms(u16 ms);
void Write595(u8 dat);
void displayNumber(u8 number);

#endif

### main.c

#include "main.h"

void main(void) {
    u8 number = 0;
    u8 key;
    u8 beep = 0;

    EAXFR = 1; // Enable XFR access
    CKCON = 0x00; // Set external data bus speed to fastest
    WTST = 0x00; // Set program read wait time to zero clocks, CPU executes program at maximum speed
    P0M1 = 0x00; P0M0 = 0x00; // Configure P0 port as quasi-bidirectional mode
    P1M1 = 0x00; P1M0 = 0x00; // Configure P1 port as quasi-bidirectional mode
    P2M1 = 0x00; P2M0 = 0xFF; // Configure P2 port as push-pull output
    
    while (1) {
        P2 = 0x7E;
        u8 temp = P2;
        temp &= 0x70;
        
        if(temp != 0x70) {
            delayms(10);
            
            if(temp != 0x70) {
                temp = P2;
                
                switch(temp) {
                    case 0x6E: key = 1; beep = 1; break;
                    case 0x5E: key = 5; beep = 1; break;
                    case 0x3E: key = 8; beep = 1; break;
                }
                
                delayms(100);
                beep = 0;
                
                while(temp != 0x70) {
                    temp = P2;
                    temp &= 0x70;
                }
            }
        }

        if(beep == 1)
            BUZZER = 1;
        else
            BUZZER = 0;

        if(key > 0 && key <= 10) {
            displayNumber(key);
            key = 0; // Reset after displaying the value
        }
        
        delayms(1);
    }
}

void delayms(u16 ms) {
    u16 i;
    
    do {
        i = MAIN_Fosc / 6000;
        while(--i);
    } while(--ms);
}

void Write595(u8 dat) {
    u16 i;
    u8 datcode = SEG_Code[dat];
    
    for(i = 0; i < 8; ++i) {
        SH = 0;
        DS = datcode & 0x80;
        SH = 1;
        datcode <<= 1;
    }
    
    ST = 0;
    ST = 1;
}

void displayNumber(u8 number) {
    Write595((u8)(number / 100));
    COM1 = 0;
    COM2 = 1;
    COM3 = 1;
    delayms(1);
    
    Write595((u8)(number / 10 % 10));
    COM1 = 1;
    COM2 = 0;
    COM3 = 1;
    delayms(1);
    
    Write595((u8)(number % 10));
    COM1 = 1;
    COM2 = 1;
    COM3 = 0;
    delayms(1);
}

上述代码实现了当检测到有效的按键按下时，通过蜂鸣器发出声音提示，并在数码管上显示对应的按键值。注意这里简化处理了部分逻辑以保持代码的清晰度。