级联下的传值方式

级联下, N个MAX7219相当于组成了一个8*N bit宽度的锁存器, 如果需要对第M个7219进行写入, 需要做M次寻址+写入后拉高CS, 才能到达这个7219. 如果仅仅对这个7219进行操作, 不操作其他7219, 那么在第1个寻址写入后, 做的寻址写入输入的都是空值.

对于级联的MAX7219, 如果要显示产生滚动的效果, 那么每次要操作的都是整行, 可以将其看成是一个(N8)8的点阵, 每次直接对一行写入N个byte.

连线

• CLK => P2.2
• CS => P2.1
• DIN => P2.0
• VCC => 5V
• GND => GND

代码示例

#include <reg52.h>
#include <intrins.h>

#define u8 unsigned char
#define u16  unsigned int

#define DECODE_MODE  0x09
#define INTENSITY    0x0A
#define SCAN_LIMIT   0x0B
#define SHUT_DOWN    0x0C
#define DISPLAY_TEST 0x0F

#define BLOCKS 4

sbit MAX7219_CLK = P2^2;
sbit MAX7219_CS  = P2^1;
sbit MAX7219_DIN = P2^0;

u8 code bytes[] = {
  0x3e,0x63,0x63,0x7f,0x63,0x63,0x63,0x63, //A
  0x7e,0x63,0x63,0x7e,0x63,0x63,0x63,0x7e, //B
  0x3e,0x63,0x63,0x60,0x60,0x63,0x63,0x3e, //C
  0x3e,0x63,0x73,0x6b,0x67,0x63,0x63,0x3e, //0
  0x0c,0x1c,0x3c,0x0c,0x0c,0x0c,0x0c,0x3f, //1
  0x3e,0x63,0x63,0x06,0x0c,0x18,0x30,0x7f, //2
  0x3e,0x63,0x63,0x0e,0x03,0x63,0x63,0x3e, //3
  0x06,0x0e,0x1e,0x36,0x66,0x7f,0x06,0x06, //4
  0x7f,0x60,0x60,0x7e,0x03,0x03,0x03,0x7e, //5
  0x3e,0x63,0x60,0x7e,0x63,0x63,0x63,0x3e, //6
  0x7f,0x03,0x03,0x06,0x0c,0x18,0x18,0x18, //7
  0x3e,0x63,0x63,0x3e,0x63,0x63,0x63,0x3e, //8
  0x3e,0x63,0x63,0x63,0x3f,0x03,0x63,0x3e, //9
};

u8 val[BLOCKS];
u8 character_len = sizeof(bytes) / 8;

void delay(u16 x)
{
  u16 i,j;
  for(i = 0; i < x; i++)
    for(j = 0;j < 112; j++);
}

void Max7219_writeByte(u8 dat)
{
  u8 i;
  MAX7219_CS = 0;
  for(i = 8; i >= 1; i--)
  {
    MAX7219_CLK = 0;
    MAX7219_DIN = dat & 0x80; // &10000000, 取最高位
    dat = dat << 1;
    MAX7219_CLK = 1;
  }
}

void Max7219_singeWrite(u8 index, u8 addr, u8 dat)
{ 
  MAX7219_CS = 0;
  Max7219_writeByte(addr);
  Max7219_writeByte(dat);
  while(index--)
  {
    Max7219_writeByte(0x00);
    Max7219_writeByte(0x00);
  }
  MAX7219_CS = 1;
}

void Max7219_multiWrite(u8 addr, u8 len, u8* dat)
{ 
  MAX7219_CS = 0;
  while(len--)
  {
    Max7219_writeByte(addr);
    Max7219_writeByte(*dat++);
  }
  MAX7219_CS = 1;
}

void Max7219_init(void)
{
  u8 i;
  for (i = 0; i < BLOCKS; i++)
  {
    Max7219_singeWrite(i, SHUT_DOWN,   0x01);  // 0x00:shutdown, 0x01:normal
    Max7219_singeWrite(i, DECODE_MODE, 0x00);  // No decode
    Max7219_singeWrite(i, INTENSITY,   0x03);  // 0x00:min, 0x0F:max
    Max7219_singeWrite(i, SCAN_LIMIT,  0x07);  // Display 8 digits
    Max7219_singeWrite(i, DISPLAY_TEST, 0x00); // 0x00:normal, 0x01:test mode
  }
}

void main(void)
{
  // pos:点阵右沿对应的val数组元素编号. 因为要无缝滚屏, 用右沿做求余不会产生跳变
  // lpos: 点阵左沿对应的val数组元素编号, 每次根据点阵右沿和点阵宽度计算得到
  u16 pos = 0, lpos = 0;
  // cpos: 点阵左沿对应的文字编号
  // bpos: 在这个文字中, 当前移动到第几个bit, 值从0-7
  u8 i, j, cpos = 0, bpos = 0, tcpos = 0;
  Max7219_init();
  while(1)
  {
    lpos = pos + sizeof(bytes) - BLOCKS * 8;
    cpos = lpos / 8; // 第几个字
    bpos = lpos % 8; // 字的第几个bit
    for (i = 0; i < 8; i++) // 对每一行, 对val的每个元素赋值
    {
      // 从第cpos个字的bpos位开始, 填满每个点阵对应的byte
      for (j = 0; j < BLOCKS; j++)
      {
        // 高位部分
        tcpos = (cpos + j) % character_len;
        val[j] = bytes[tcpos * 8 + i] << bpos;
        // 低位部分
        tcpos = (cpos + j + 1) % character_len;
        val[j] |= bytes[tcpos * 8 + i] >> (8 - bpos);
      }
      Max7219_multiWrite(i+1, BLOCKS, val);
    }
    // 每处理完一屏, pos右移一位
    pos = (pos + 1) % sizeof(bytes);
    delay(50);
  }
}

参考

• 一个好用的8x8 LED编辑器 https://xantorohara.github.io/led-matrix-editor

STC89C52驱动MAX7219LED点阵级联, 文字滚动效果