在LCD上显示一个6x8的字符，字库格式是这样的
unsigned char code Font_code[][6] = {
{0x00,0x00,0x00,0x00,0x00,0x00},// (0)
{0x00,0x00,0x00,0x4F,0x00,0x00},//!(1)
{0x00,0x00,0x07,0x00,0x07,0x00},//"(2)
{0x00,0x14,0x7F,0x14,0x7F,0x14},//#(3)
{0x00,0x24,0x2A,0x7F,0x2A,0x12},//$(4)
{0x00,0x23,0x13,0x08,0x64,0x62},//%(5)
{0x00,0x36,0x49,0x55,0x22,0x50},//&(6)
{0x00,0x00,0x05,0x03,0x00,0x00},//'(7)
{0x00,0x00,0x1C,0x22,0x41,0x00},//((8)
{0x00,0x00,0x41,0x22,0x1C,0x00},//)(9)
{0x00,0x14,0x08,0x3E,0x08,0x14},//*(10)
{0x00,0x08,0x08,0x3E,0x08,0x08},//+(11)
{0x00,0x00,0x50,0x30,0x00,0x00},//,(12)
{0x00,0x08,0x08,0x08,0x08,0x08},//-(13)
{0x00,0x00,0x60,0x60,0x00,0x00},//.(14)
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}
程序中调用（显示6x8的字符）
void print6x8c(unsigned char x, unsigned char y, unsigned char c_dat)
{
        unsigned char i;
        c_dat -= 32;                //查表
        x *= 6;                                //宽6

        LCD_pos_byte(x, y);        //坐标
        for(i = 0; i < 6; i++) LCD_write_dat(Font_code[c_dat][i]);       
}

请问这个c_dat -= 32;为啥要-32？