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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 --*/
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
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0x38,0x38,0x38,0x38,0x38,0x38,0x00,0x00,0xF8,0xF8,0xF8,0x38,0x38,0x38,0x38,0x78,
0xF8,0xF0,0xE0,0x00,0x00,0x80,0xE0,0xF0,0xF0,0x78,0x38,0x38,0x38,0x38,0x78,0xF0,
0xF0,0x40,0x00,0x00,0x00,0x00,0xC0,0xF8,0xF8,0x38,0xF8,0xF8,0xC0,0x00,0x00,0x00,
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0xF0,0xE0,0xC0,0xC0,0xC0,0xE0,0xF0,0xFF,0x7F,0x1F,0x00,0x00,0x31,0xF3,0xF7,0xE7,
0xC7,0xC6,0xCE,0xCE,0xFC,0xFC,0x78,0x00,0x00,0xFF,0xFF,0xFF,0x07,0x07,0x07,0x07,
0x07,0xFF,0xFF,0xFF,0x00,0x00,0x1C,0x1C,0x1C,0x1C,0x1C,0x00,0xFF,0xFF,0xFF,0x07,
0x07,0x07,0x07,0x07,0x07,0x00,0x00,0x00,0xFF,0xFF,0xFF,0x0E,0x0E,0x0E,0x0E,0x0F,
0x0F,0x07,0x03,0x00,0x00,0x1F,0x7F,0xFF,0xF0,0xE0,0xC0,0xC0,0xDC,0xDC,0xDC,0xFC,
0xFC,0x7C,0x00,0x80,0xF0,0xFE,0x7F,0x3F,0x39,0x38,0x39,0x3F,0x7F,0xFE,0xF0,0x80,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
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0x01,0x01,0x01,0x01,0x01,0x00,0x00,0x00,0x00,0x01,0x01,0x01,0x00,0x00,0x00,0x00,
0x00,0x01,0x01,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x01,0x00,
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0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x01,0x01,0x01,0x01,0x00,
0x00,0x00,0x00,0x01,0x01,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x01,
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0xF8,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x80,0xC0,0x60,0x38,0x38,0x60,0xC0,0x80,
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0xF0,0x10,0x10,0x10,0x10,0x00,0x00,0x80,0xF0,0xF0,0x80,0x80,0xF8,0xF8,0x80,0x90,
0xB0,0xE0,0xE0,0x80,0x80,0x80,0x00,0x80,0x80,0x80,0xF8,0xF8,0x80,0x80,0xF0,0xF0,
0x10,0x10,0x18,0x08,0x08,0x08,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
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0xA9,0xA0,0x20,0x00,0x02,0x02,0x13,0x11,0x53,0xD2,0x92,0xFE,0xFE,0x12,0xD2,0xD2,
0x13,0x13,0x03,0x01,0x00,0x02,0x02,0x02,0x82,0xE2,0x7F,0x1F,0x02,0x02,0x02,0xFF,
0xFF,0x02,0x02,0x02,0x02,0x00,0x00,0x00,0x81,0xC1,0x78,0x3F,0x3F,0x74,0xC4,0xC4,
0x7C,0x3C,0x00,0x00,0x00,0x00,0x00,0x20,0x38,0x1E,0xFF,0xFF,0x8E,0xFC,0x7F,0x0F,
0x8F,0xDD,0x71,0xFD,0x8F,0x03,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
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0x02,0x02,0x02,0x02,0x00,0x00,0x02,0x03,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x03,
0x03,0x00,0x00,0x00,0x00,0x00,0x02,0x03,0x01,0x04,0x04,0x06,0x02,0x03,0x01,0x01,
0x01,0x03,0x06,0x06,0x02,0x00,0x00,0x00,0x00,0x00,0x03,0x03,0x00,0x00,0x02,0x03,
0x01,0x00,0x00,0x01,0x03,0x03,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
};
//-----------------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…