【连载】【FPGA黑金开发板】NIOSII那些事儿LCD驱动及图片显示（二十二）

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简介     

      这一节，我们来讲解与点阵LCD相关的内容，主要介绍硬件结构及其驱动编写。

      做我们这行的，我相信很少有人不知道点阵LCD的，就算没用过也应该见过（俗话说，没吃过猪肉还没见过猪跑啊，呵呵）。不用我多说，大家也知道这东西是做什么用的。不过可能很多人对他的结构还不是很熟悉。通常我们所见到的LCD模块具有LCM(玻璃)、背光、PCB板。其实这三样只有一样是必须要有的，那就是LCM（玻璃）。大家就有点疑问了，没有背光无所谓了，那没有PCB板，就一块玻璃有啥用啊。大家接着听我说，点阵的LCD模块按驱动控制器的集成方式，分为两种：COB和COG，COG就是将驱动控制芯片集成到了玻璃里面，我们只需要在电路板上加上无法集成的电容电阻就可以了；而COB是那种需要将驱动芯片焊接在LCD模块后面的PCB板上的。这回大家应该明白为什么只有一块玻璃就能显示了吧。

      在我们黑金开发板上使用的LCD就是128*64的COG液晶，它将驱动控制IC集成到了LCM上，这样就省去了PCB底板，给我们节省了很大的空间。下面，我简单介绍一下这款液晶的一些参数，如下图所示，它的驱动芯片为ST7565P。支持三种接口方式，我们采用的是串行时序方式，接口简单，使用方便，相比其他两种，也节省了很多的管脚。

      下图为LCD的串行接口原理图，大家可以看到，仅四根线就可以搞定了。

      对于LCD而言，需要清楚的了解驱动控制IC的显存与LCD上的点的对应关系，这一点非常重要。通过下图，我们可以了解到，LCD的显存中存在8（page）*8+1行，即65行，s0-s131，即132列，而液晶只有64*128个点。因此显存上的一些数据是不能显示的。通过实验测试得知，最后一行（page8中的D0）和最后三列（ADC为正常时，s129、s130、s131；ADC为反向时，s0、s1、s2）是不能显示的，而显存上其他数据与LCD上的点一一对应。如下图的红圈处所示的区域。

      显示屏上的每一个点都对应有控制器片内的显示缓存RAM中的一个位， 显示屏上64*128个点分别对应着显示RAM的8个Page， 每一个Page有128个byte的空间对应，如下表所示

      大家如要点亮 LCD 屏上的某一个点时，实际上就是对该点所对应的显示 RAM 区中的某一个位进行置 1 操作；所以就要确定该点所处的行地址、列地址。从上图中可以看出，液晶的行地址实际上就是 Page 的信息，每一个 Page应有 8 行；而列地址则表示该点的横坐标，在屏上为从左到右排列，Page 中的一个 Byte 对应的是一列（8行，即 8 个点） ，达 128列。 可以根据这样的关系在程序中控制 LCD显示屏的显示。

硬件设置     

      下面我们来看，如果如何在NIOS下驱动液晶屏。首先，我们需要在软核中四个PIO口，分别对应LCD的四个引脚。如下图所示，四个PIO模块全部为输出。

      建好以后，自动分配地址，中断，编译…

      然后，我们回到Quartus中，通过TCL脚本分配好管脚疑惑，LCD部分如下图示是

      接着又是编译，完成以后，硬件部分的设置就结束了。

软件开发

      接下来，我们打开NIOS IDE软件。

      第一步做的还是需要进行一次完全编译，Ctrl+b，漫长的等待…

      编译完成后，我们进入system.h，查看是否有我们想要得到的LCD部分，如下表所示

/*
 * LCD_SI configuration
 *
 */

#define LCD_SI_NAME "/dev/LCD_SI"
#define LCD_SI_TYPE "altera_avalon_pio"
#define LCD_SI_BASE 0x000018b0
…
/*
 * LCD_A0 configuration
 *
 */

#define LCD_A0_NAME "/dev/LCD_A0"
#define LCD_A0_TYPE "altera_avalon_pio"
#define LCD_A0_BASE 0x000018c0
…
/*
 * LCD_SCL configuration
 *
 */

#define LCD_SCL_NAME "/dev/LCD_SCL"
#define LCD_SCL_TYPE "altera_avalon_pio"
#define LCD_SCL_BASE 0x000018d0
…
/*
 * LCD_CS configuration
 *
 */

#define LCD_CS_NAME "/dev/LCD_CS"
#define LCD_CS_TYPE "altera_avalon_pio"
#define LCD_CS_BASE 0x000018e0
…

接下来，我们需要在sopc.h中添加LCD部分的代码

typedef struct
{
    unsigned long int DATA;
    unsigned long int DIRECTION;
    unsigned long int INTERRUPT_MASK;
    unsigned long int EDGE_CAPTURE;
    
}PIO_STR;

#define _LCD

#ifdef _LCD
#define LCD_CS            ((PIO_STR *) LCD_CS_BASE)
#define LCD_SCL           ((PIO_STR *) LCD_SCL_BASE)
#define LCD_A0            ((PIO_STR *) LCD_A0_BASE)
#define LCD_SI            ((PIO_STR *) LCD_SI_BASE)
#endif /* _LCD */

接下来，我们根据LCD串行方式的时序图来编写LCD的驱动，时序图如下图所示

      我们需要在工程目录中的driver下建立lcd.c文件，代码如下

/*
 * =================================================================
 *       Filename:  lcd.c
 *   Description:  LCD驱动
 *        Version:  1.0.0
 *        Created:  2010.4.16
 *       Revision:  none
 *       Compiler:  Nios II 9.0 IDE
 *         Author:  马瑞 (AVIC)
 *          Email:  avic633@gmail.com  
 * ==================================================================
 */

/*-------------------------------------------------------------------
 *  Include
 *-----------------------------------------------------------------*/
#include "system.h"
#include <unistd.h>
#include "../inc/sopc.h"

/*------------------------------------------------------------------
 *  Variable
 *-----------------------------------------------------------------*/
unsigned char buf[]={
//这是一张128*64的图片转换而成
/*--  宽度x高度=128x64  --*/
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};
//-----------------Function Prototype--------------------//
void initialize_lcd(void);
void draw_screen(unsigned char *p);
void clear(void);
void write_data(unsigned char dat);
void data_send(unsigned char dat); 
void write_command(unsigned char com);

/* 
 * ===  FUNCTION  ==================================================
 *         Name:  data_send
 *  Description:  发送一个字节数据
 * =================================================================
 */
void data_send(unsigned char dat)
{
    unsigned char i;

    LCD_CS->DATA=0;
    LCD_SCL->DATA=0;

    for(i=0;i<8;i++){
        if(dat&0x80)LCD_SI->DATA=1;
        else LCD_SI->DATA=0;
        
        dat<<=1;

        LCD_SCL->DATA=0;

        LCD_SCL->DATA=1;
    }

    LCD_CS->DATA=1;
}

/* 
 * ===  FUNCTION  ===================================================
 *         Name:  write_command
 *  Description: A0为低时，写命令字，
 * =================================================================
 */
void write_command(unsigned char com)
{
    LCD_A0->DATA=0;

    data_send(com);
}

/* 
 * ===  FUNCTION  ===================================================
 *         Name:  write_data
 *  Description:  A0为高时，写数据
 * =================================================================
 */
void write_data(unsigned char dat)
{
    LCD_A0->DATA = 1;

    data_send(dat);
}
/* 
 * ===  FUNCTION  ===================================================
 *         Name:  set_x
 *  Description:  设置列地址
 * =================================================================
 */
void set_x(unsigned char x)
{
    write_command(x>>4|0x10);
    write_command(x&0xf);
}
/* 
 * ===  FUNCTION  ===================================================
 *         Name:  set_y
 * Description:  设置页地址 一共8页
 * =================================================================
 */
void set_y(unsigned char y)
{
    write_command(y|0xb0);
}
/* 
 * ===  FUNCTION  ===================================================
 *         Name:  clear
 * Description:  清屏
 * =================================================================
 */
void clear(void)
{
    int seg;
    int page;

    for(page=0;page<8;page++) {
        set_y(page);//设置页地址，一共8页
        set_x(0x00);//设置列地址为0

        for(seg=0;seg<128;seg++){
            write_data(0); 
        }
    }
}
/* 
 * ===  FUNCTION  ===================================================
 *         Name:  draw_screen
 * Description:  显示一张128*64的图片
 * =================================================================
 */
void draw_screen(unsigned char *p)
{
    int seg;
    int page;

    for(page=0;page<8;page++) {
        set_y(page);//设置页地址，一共8页
        set_x(0x00);//设置列地址为0

        for(seg=0;seg<128;seg++){
            write_data(*p++); 
        }
    }
}
/* 
 * ===  FUNCTION  ===================================================
 *         Name:  initialize_lcd
 * Description:  LCD初始化，初始化函数由厂商提供，相关设置请查询datasheet
 * =================================================================
 */
void initialize_lcd(void)
{
    write_command(0xaf); //ON DISPLAY
    write_command(0x40); //STAR DISPLAY
    write_command(0xa0); //ADC NORMAL
    write_command(0xa6); //Display Normal
    write_command(0xa4); //CLEAR
    write_command(0xa2); //1/9BIAS
    write_command(0xc8); //COMMON OUTPUT DIRECTION
    write_command(0x2f); //POWER CONTROL
    write_command(0x24); //RESISTER RATIO
    write_command(0x81); //VOLUM MODE SET
    write_command(0x24); //RESISTER RATIO
}

写好驱动以后，我们还需要在工程目录的inc下建立lcd.h函数，代码如下：

/*
 * =================================================================
 *       Filename:  lcd.h
 *   Description:  
 *        Version:  1.0.0
 *        Created:  2010.4.16
 *       Revision:  none
 *       Compiler:  Nios II 9.0 IDE
 *         Author:  马瑞 (AVIC)
 *          Email:  avic633@gmail.com  
 * =================================================================
 */

#ifndef _lcd_h_
#define _lcd_h_

extern void initialize_lcd(void);
extern void draw_screen(unsigned char *p);
extern void clear(void);
extern unsigned char buf[];

#endif //_lcd_h_

接下来，需要做的就是写个测试函数，在main.c中添加如下代码

/*
 * =================================================================
 *       Filename:  main.c
 *   Description:  LCD试验，在LCD上打印128*64图片
 *        Version:  1.0.0
 *        Created:  2010.4.16
 *       Revision:  none
 *       Compiler:  Nios II 9.0 IDE
 *         Author:  马瑞 (AVIC)
 *          Email:  avic633@gmail.com  
 * =================================================================
 */

/*------------------------------------------------------------------
 *  Include
 *-----------------------------------------------------------------*/
#include "../inc/lcd.h"

/* 
 * ===  FUNCTION  ===================================================
 *         Name:  main
 *  Description:  
 * =================================================================
 */
int main(void)
{
    initialize_lcd();
    clear();
    draw_screen(buf);
    
}

      OK，代码就全部写好了。编译之后将程序下载进去，我们就可以看出效果了，如下图所示，显示的效果还是很不错的。

      上面涉及到了一个放置图片的数组，这个数组是通过点阵液晶取模软件生成的。我下面简单介绍一下它的使用方法。

      首先打开点阵液晶取模软件，如下图所示

如果想显示128*64的图片，首先就要有一个分辨率为128*64的图片，然后按打开图像图标，如下图所示红圈处，将图片载入

然后按下图所示红圈1，点击取模方式。然后点击红圈2，这时在红圈3处就会生成我们需要的16进制的代码了。操作很简单，软件里面还有很多功能，大家可以自行研究一下。

好了，这一节我们就讲完了。下一节，我们将在这一节的基础上，研究有关中文显示和英文变宽字体显示的方法，敬请期待…