原创 【原创】基于Nios II的VGA字符显示控制

Nios II嵌入式系统硬件设计（四）

在上一篇文章 基于Verilog的VGA显示控制 中介绍了使用纯硬件（Verilog）方法实现的VGA显示控制，不过上述方法只能显示静态的图像，不能更改，也不能显示字符，在本文中介绍一种基于Nios II的VGA字符显示控制，可以显示所有ASCII字符，显示图像可更改，便把分辨率改成了32*24。

模块框图如下：

VGA控制器的设计和显存（RAM）的设计与 基于Verilog的VGA显示控制 中的基本相同，只是显存用双口RAM替换了单口ROM，以便于修改显示内容。关键在于Nios II处理器中的设计。

       按照正常流程设计，需要将显存（RAM）加上Avalon slave接口挂到Avalon的互联结构上，在本设计中，为了偷懒，没有编写Avalon slave接口，直接用SOPC的PIO与显存（RAM）连接，通过直接读写PIO来改变显存中存储的颜色值。

       为了在LCD上显示各种字符，需要在Nios II的存储器中存储所有字符的字模表。

unsigned char CHTAB[][5]=<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

{

{0x00, 0x00, 0x00, 0x00, 0x00}, //" "=00h

{0x00, 0x00, 0x<?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />4F, 0x00, 0x00}, //"!"=01h

{0x00, 0x07, 0x00, 0x07, 0x00}, //"""=02h

{0x14, 0x7F, 0x14, 0x7F, 0x14}, //"#"=03h

{0x24, 0x2A, 0x7F, 0x2A, 0x12}, //"$"=04h

{0x23, 0x13, 0x08, 0x64, 0x62}, //"%"=05h

{0x36, 0x49, 0x55, 0x22, 0x50}, //"&"=06h

{0x00, 0x05, 0x03, 0x00, 0x00}, //"'"=07h

{0x00, 0x1C, 0x22, 0x41, 0x00}, //"("=08h

{0x00, 0x41, 0x22, 0x1C, 0x00}, //")"=09h

{0x14, 0x08, 0x3E, 0x08, 0x14}, //"*"=0Ah

{0x08, 0x08, 0x3E, 0x08, 0x08}, //"+"=0Bh

{0x00, 0x50, 0x30, 0x00, 0x00}, //","=0Ch

{0x08, 0x08, 0x08, 0x08, 0x08}, //"-"=0Dh

{0x00, 0x60, 0x60, 0x00, 0x00}, //"."=0Eh

{0x20, 0x10, 0x08, 0x04, 0x02}, //"/"=0Fh

{0x3E, 0x51, 0x49, 0x45, 0x3E}, //"0"=10h

{0x00, 0x42, 0x7F, 0x40, 0x00}, //"1"=11h

{0x42, 0x61, 0x51, 0x49, 0x46}, //"2"=12h

{0x21, 0x41, 0x45, 0x4B, 0x31}, //"3"=13h

{0x18, 0x14, 0x12, 0x7F, 0x10}, //"4"=14h

{0x27, 0x45, 0x45, 0x45, 0x39}, //"5"=15h

{0x3C, 0x4A, 0x49, 0x49, 0x30}, //"6"=16h

{0x01, 0x01, 0x79, 0x05, 0x03}, //"7"=17h

{0x36, 0x49, 0x49, 0x49, 0x36}, //"8"=18h

{0x06, 0x49, 0x49, 0x29, 0x1E}, //"9"=19h

{0x00, 0x36, 0x36, 0x00, 0x00}, //":"=1Ah

{0x00, 0x56, 0x36, 0x00, 0x00}, //";"=1Bh

{0x08, 0x14, 0x22, 0x41, 0x00}, //"<"=1Ch

{0x14, 0x14, 0x14, 0x14, 0x14}, //"="=1Dh

{0x00, 0x41, 0x22, 0x14, 0x08}, //">"=1Eh

{0x02, 0x01, 0x51, 0x09, 0x06}, //"?"=1Fh

{0x32, 0x49, 0x79, 0x41, 0x3E}, //"@"=20h

{0x7E, 0x11, 0x11, 0x11, 0x7E}, //"A"=21h

{0x41, 0x7F, 0x49, 0x49, 0x36}, //"B"=22h

{0x3E, 0x41, 0x41, 0x41, 0x22}, //"C"=23h

{0x41, 0x7F, 0x41, 0x41, 0x3E}, //"D"=24h

{0x7F, 0x49, 0x49, 0x49, 0x49}, //"E"=25h

{0x7F, 0x09, 0x09, 0x09, 0x01}, //"F"=26h

{0x3E, 0x41, 0x41, 0x49, 0x7A}, //"G"=27h

{0x7F, 0x08, 0x08, 0x08, 0x7F}, //"H"=28h

{0x00, 0x41, 0x7F, 0x41, 0x00}, //"I"=29h

{0x20, 0x40, 0x41, 0x3F, 0x01}, //"J"=2Ah

{0x7F, 0x08, 0x14, 0x22, 0x41}, //"K"=2Bh

{0x7F, 0x40, 0x40, 0x40, 0x40}, //"L"=2Ch

{0x7F, 0x02, 0x0C, 0x02, 0x7F}, //"M"=2Dh

{0x7F, 0x06, 0x08, 0x30, 0x7F}, //"N"=2Eh

{0x3E, 0x41, 0x41, 0x41, 0x3E}, //"O"=2Fh

{0x7F, 0x09, 0x09, 0x09, 0x06}, //"P"=30h

{0x3E, 0x41, 0x51, 0x21, 0x5E}, //"Q"=31h

{0x7F, 0x09, 0x19, 0x29, 0x46}, //"R"=32h

{0x26, 0x49, 0x49, 0x49, 0x32}, //"S"=33h

{0x01, 0x01, 0x7F, 0x01, 0x01}, //"T"=34h

{0x3F, 0x40, 0x40, 0x40, 0x3F}, //"U"=35h

{0x1F, 0x20, 0x40, 0x20, 0x1F}, //"V"=36h

{0x7F, 0x20, 0x18, 0x20, 0x7F}, //"W"=37h

{0x63, 0x14, 0x08, 0x14, 0x63}, //"X"=38h

{0x07, 0x08, 0x70, 0x08, 0x07}, //"Y"=39h

{0x61, 0x51, 0x49, 0x45, 0x43}, //"Z"=3Ah

{0x00, 0x7F, 0x41, 0x41, 0x00}, //"["=3Bh

{0x02, 0x04, 0x08, 0x10, 0x20}, //"\"=3Ch

{0x00, 0x41, 0x41, 0x7F, 0x00}, //"]"=3Dh

{0x04, 0x02, 0x01, 0x02, 0x04}, //"^"=3Eh

{0x40, 0x40, 0x40, 0x40, 0x40}, //"_"=3Fh

{0x01, 0x02, 0x04, 0x00, 0x00}, //"`"=40h

{0x20, 0x54, 0x54, 0x54, 0x78}, //"a"=41h

{0x7F, 0x48, 0x44, 0x44, 0x38}, //"b"=42h

{0x38, 0x44, 0x44, 0x44, 0x28}, //"c"=43h

{0x38, 0x44, 0x44, 0x48, 0x7F}, //"d"=44h

{0x38, 0x54, 0x54, 0x54, 0x18}, //"e"=45h

{0x00, 0x08, 0x7E, 0x09, 0x02}, //"f"=46h

{0x0C, 0x52, 0x52, 0x4C, 0x3E}, //"g"=47h

{0x7F, 0x08, 0x04, 0x04, 0x78}, //"h"=48h

{0x00, 0x44, 0x7D, 0x40, 0x00}, //"i"=49h

{0x20, 0x40, 0x44, 0x3D, 0x00}, //"j"=4Ah

{0x00, 0x7F, 0x10, 0x28, 0x44}, //"k"=4Bh

{0x00, 0x41, 0x7F, 0x40, 0x00}, //"l"=4Ch

{0x7C, 0x04, 0x78, 0x04, 0x78}, //"m"=4Dh

{0x7C, 0x08, 0x04, 0x04, 0x78}, //"n"=4Eh

{0x38, 0x44, 0x44, 0x44, 0x38}, //"o'=4Fh

{0x7E, 0x0C, 0x12, 0x12, 0x0C}, //"p"=50h

{0x0C, 0x12, 0x12, 0x0C, 0x7E}, //"q"=51h

{0x7C, 0x08, 0x04, 0x04, 0x08}, //"r"=52h

{0x58, 0x54, 0x54, 0x54, 0x64}, //"s"=53h

{0x04, 0x3F, 0x44, 0x40, 0x20}, //"t"=54h

{0x3C, 0x40, 0x40, 0x3C, 0x40}, //"u"=55h

{0x1C, 0x20, 0x40, 0x20, 0x1C}, //"v"=56h

{0x3C, 0x40, 0x30, 0x40, 0x3C}, //"w"=57h

{0x44, 0x28, 0x10, 0x28, 0x44}, //"x"=58h

{0x1C, 0xA0, 0xA0, 0x90, 0x7C}, //"y"=59h

{0x44, 0x64, 0x54, 0x4C, 0x44}, //"z"=5Ah

{0x00, 0x08, 0x36, 0x41, 0x00}, //"{"=5Bh

{0x00, 0x00, 0x77, 0x00, 0x00}, //"|"=5Ch

{0x00, 0x41, 0x36, 0x08, 0x00}, //"}"=5Dh

{0x02, 0x01, 0x02, 0x04, 0x02}, //"~"=5Fh

{0x7F, 0x7F, 0x7F, 0x7F, 0x7F} //" "=60h

};

显示像素函数，负责向显存中写入指定行和列的颜色值，这里通过读写PIO来进行操作。

void Pixel(unsigned char row, unsigned char column, unsigned char color)

{

unsigned short offset;

offset = row * 32 + column;//根据行列数值计算显存中的便宜地址

IOWR_ALTERA_AVALON_PIO_DATA(WRADDRESS_BASE,offset);//输出显存地址

IOWR_ALTERA_AVALON_PIO_DATA(DATA_BASE,color);//输出改点的颜色值

IOWR_ALTERA_AVALON_PIO_DATA(WREN_BASE,1);

IOWR_ALTERA_AVALON_PIO_DATA(WRCLOCK_BASE,1);//时钟上升沿写入数据

IOWR_ALTERA_AVALON_PIO_DATA(WRCLOCK_BASE,0);

IOWR_ALTERA_AVALON_PIO_DATA(WREN_BASE,0);

}

清屏函数，是全屏显示成黑色

void ClearScreen(void)

{

unsigned char p,q;

for(p = 0; p < 24; p++ )

{

    for(q = 0; q < 32; q++)

    {

        Pixel(p,q,0);

    }

}

}

字符显示函数

void Character(unsigned char row, unsigned char column, unsigned char *CH, unsigned char frontcolor, unsigned char backcolor)

{

unsigned char i, h, color;

for(h = 0; h < 5; h ++) //遍历字模占用的5个字节

{

for(i = 0; i < 8; i ++) //遍历字模中每个字节的8个bit

{

if(1 == ((*(CH + h) >> i) & 1))

{

color = frontcolor; //如果某bit为1，则显示前景颜色

}

else

{

color = backcolor; //如果某bit为0，则显示背景颜色值

}

Pixel(row + i, column + h, color); //显示像素

}

}

}

Main函数，首先清屏，然后在屏幕上分三行显示0123456789ABCDEFGH

Int main（）

{

ClearScreen();

 Character(0,0,CHTAB[16],7,0);//blue first line

 Character(0,5,CHTAB[17],164,0);

 Character(0,10,CHTAB[18],56,0);//green

 Character(0,15,CHTAB[19],199,0);

 Character(0,20,CHTAB[20],192,0);//red

 Character(0,25,CHTAB[21],255,0);

 Character(8,0,CHTAB[22],63,0);//second line

 Character(8,5,CHTAB[23],248,0);

 Character(8,10,CHTAB[24],199,0);

 Character(8,15,CHTAB[25],56,0);

 Character(8,20,CHTAB[33],248,0);

 Character(8,25,CHTAB[34],182,0);

 Character(16,0,CHTAB[35],164,0);//third line

 Character(16,5,CHTAB[36],7,0);

 Character(16,10,CHTAB[37],248,0);

 Character(16,15,CHTAB[38],182,0);

 Character(16,20,CHTAB[39],255,0);

 Character(16,25,CHTAB[40],199,0);

  return 0;

}

下面是程序运行结果。