PIC单片机利用视觉暂留现象显示字符

Persistance of Vision (PoV)， 即视觉暂留现象， 人眼在观察景物时，光信号传人大脑神经，需经过一段短暂的时间，光的作用结束后，视觉形象并不立即消失，这种残留的视觉称“后像”，视觉的这一现象则被称为“视觉暂留”。其具体应用是电影的拍摄和放映。原因是由视神经的反应速度造成的.其时值是二十四分之一秒。是动画、电影等视觉媒体形成和传播的根据。

利用PoV，还可以制作电子小玩意，比如利用几个LED，就能显示图案，字符等。

下面是一个利用PoV显示时钟的例子：



下面是一段利用PoV显示字符的PIC单片机程序，利用CCS C编译器编译：

主程序文件： pov.c


#include <16F877A.h>


#include "font.h"


#include "font.c"



#fuses HS,NOWDT,NOPROTECT,NOLVP /* DONNOT use WDT */



/* Port D drives the LEDs */


#use fast_io(D)



#use delay(clock = 4000000) /* the crystal frequency is 4.000 MHz*/



void display_string(int8 *str)


{


int8 font_matrix_buf[FONT_WIDTH];


int8 i, j;




for(i = 0; str[i] != 0; i++)


{


get_font_matrix(str[i], font_matrix_buf);


for(j = 0; j < FONT_WIDTH; j++)


{


output_d(font_matrix_buf[j]); /* output the dots */


delay_ms(5); /* delay some time */


}


output_d(0x00);


delay_ms(5);


}


}



/**********************************************************


Description:


The entry point of the whole program.


Parameters:


None.


Return Value:


None.


Note:


N/A.


Date:


2006-04-02


**********************************************************/


void main(void)


{


int8 string[]= {'C', 'h', 'i', 'n', 'a', 0x00};



set_tris_d(0x00); /* set portD to output mode */



while(1)


{


display_string(string);


delay_ms(200);


}


}

字模头文件： font.h


#ifndef FONT_H


#define FONT_H



#define FONT_WIDTH 5



/*


CCS C doesn't support double-byte array subscript. so we must put the font table


in different arrays.


*/


#define FONT_BLANK_TABLE_SIZE (1 * FONT_WIDTH)


#define FONT_NUMBER_TABLE_SIZE (10 * FONT_WIDTH)


#define FONT_UPPER_CASE_TABLE_SIZE (26 * FONT_WIDTH)


#define FONT_LOWER_CASE_TABLE_SIZE (26 * FONT_WIDTH)



void get_font_matrix(int8 ascii_code, int8 *buf);




#endif

字模c文件： font.c


/********************************************************************


*8*8ASC码字模头文件


*右转90度ASC字模


*Modify:2005-3-16 14:31


********************************************************************/



const int8 font_blank_table[FONT_BLANK_TABLE_SIZE] = {


0x00,0x00,0x00,0x00,0x00// blank


};



const int8 font_number_table[FONT_NUMBER_TABLE_SIZE] = {


0x7C,0xA2,0x92,0x8A,0x7C,// 0


0x00,0x84,0xFE,0x80,0x00,// 1


0xC4,0xA2,0x92,0x8A,0x84,// 2


0x42,0x82,0x8A,0x96,0x62,// 3


0x30,0x28,0x24,0xFE,0x20,// 4


0x4E,0x8A,0x8A,0x8A,0x72,// 5


0x78,0x94,0x92,0x92,0x60,// 6


0x02,0xE2,0x12,0x0A,0x06,// 7


0x6C,0x92,0x92,0x92,0x6C,// 8


0x0C,0x92,0x92,0x52,0x3C// 9


};



const int8 font_uletter_table[FONT_UPPER_CASE_TABLE_SIZE] = {


0xFC,0x22,0x22,0x22,0xFC,// A


0xFE,0x92,0x92,0x92,0x6C,// B


0x7C,0x82,0x82,0x82,0x44,// C


0xFE,0x82,0x82,0x44,0x38,// D


0xFE,0x92,0x92,0x92,0x82,// E


0xFE,0x12,0x12,0x12,0x02,// F


0x7C,0x82,0x92,0x92,0x74,// G


0xFE,0x10,0x10,0x10,0xFE,// H


0x00,0x82,0xFE,0x82,0x00,// I


0x40,0x80,0x82,0x7E,0x02,// J


0xFE,0x10,0x28,0x44,0x82,// K


0xFE,0x80,0x80,0x80,0x80,// L


0xFE,0x04,0x18,0x04,0xFE,// M


0xFE,0x08,0x10,0x20,0xFE,// N


0x7C,0x82,0x82,0x82,0x7C,// O


0xFE,0x12,0x12,0x12,0x0C,// P


0x7C,0x82,0xA2,0x42,0xBC,// Q


0xFE,0x12,0x32,0x52,0x8C,// R


0x4C,0x92,0x92,0x92,0x64,// S


0x02,0x02,0xFE,0x02,0x02,// T


0x7E,0x80,0x80,0x80,0x7E,// U


0x3E,0x40,0x80,0x40,0x3E,// V


0x7E,0x80,0x70,0x80,0x7E,// W


0xC6,0x28,0x10,0x28,0xC6,// X


0x0E,0x10,0xE0,0x10,0x0E,// Y


0xC2,0xA2,0x92,0x8A,0x86// Z


};



const int8 font_lletter_table[FONT_LOWER_CASE_TABLE_SIZE] = {


0x40,0xA8,0xA8,0xA8,0xF0,// a


0xFE,0x88,0x88,0x88,0x70,// b


0x70,0x88,0x88,0x88,0x88,// c


0x70,0x88,0x88,0x88,0xFE,// d


0x70,0xA8,0xA8,0xA8,0x10,// e


0x08,0x08,0xFC,0x0A,0x0A,// f


0x10,0xA8,0xA8,0xA8,0x78,// g


0xFE,0x10,0x08,0x08,0xF0,// h


0x00,0x88,0xFA,0x80,0x00,// i


0x40,0x80,0x88,0x7A,0x00,// j


0xFE,0x20,0x50,0x88,0x00,// k


0x00,0x82,0xFE,0x80,0x00,// l


0xF8,0x08,0xF8,0x08,0xF0,// m


0xF8,0x10,0x08,0x08,0xF0,// n


0x70,0x88,0x88,0x88,0x70,// o


0xF8,0x28,0x28,0x28,0x10,// p


0x10,0x28,0x28,0x28,0xF8,// q


0xF8,0x10,0x08,0x08,0x00,// r


0x90,0xA8,0xA8,0xA8,0x48,// s


0x08,0x08,0x7E,0x88,0x88,// t


0x78,0x80,0x80,0x40,0xF8,// u


0x38,0x40,0x80,0x40,0x38,// v


0x78,0x80,0x60,0x80,0x78,// w


0x88,0x50,0x20,0x50,0x88,// x


0x18,0xA0,0xA0,0xA0,0x78,// y


0x88,0xC8,0xA8,0x98,0x88// z


};



void get_font_matrix(int8 ascii_code, int8 *buf)


{


int8 i;


int8 base;



if(ascii_code == ' ')


{


for(i=0, base=0; i < FONT_WIDTH; i++)


{


*(buf+i) = font_blank_table[base + i];


}


}


else if(ascii_code >= '0' && ascii_code <= '9')


{


for(i=0, base = (ascii_code - '0') * FONT_WIDTH; i < FONT_WIDTH; i++)


{


*(buf+i) = font_number_table[base + i];


}


}


else if(ascii_code >= 'A' && ascii_code <= 'Z')


{


for(i=0, base = (ascii_code - 'A') * FONT_WIDTH; i < FONT_WIDTH; i++)


{


*(buf+i) = font_uletter_table[base + i];


}


}


else


{


for(i=0, base = (ascii_code - 'a') * FONT_WIDTH; i < FONT_WIDTH; i++)


{


*(buf+i) = font_uletter_table[base + i];


}


}


}

这段程序会在PIC单片机的Port D点亮一排LED，用手晃动这排LED，就会看到“china”字样。

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