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학교에서 아두이노를 공부하고 있는 학생 입니다

아두이노 8x8 MATRIX LED 모듈을 이용하여 글자를 띄우고

{0,0,0,1,1,0,0,0},  EX)  8x8 MATRIX LED 모듈 문자 A의 배열 define A
{0,0,1,0,0,1,0,0},
{0,0,1,0,0,1,0,0},
{0,1,1,1,1,1,1,0},
{0,1,0,0,0,0,1,0},
{0,1,0,0,0,0,1,0},
{0,1,0,0,0,0,1,0};

왼쪽으로이동하는 소스 작업 하기위하는데 주석을 다는중에

90% 거의해결하였는데 이해가 안되는 void 함수가 1개 있어서

여기서질문드리게 되었습니다

밑에 소스에 이해가 안되는 부분에 대해서 빨간색으로 글자를 바꾸었습니다.

1. if ( gDisplayIntervalCounter < gDisplayInterval)          
   return;  여기서 return 을하게되면 어떻게 되나요 ?

2. void SetMatrixChar 의 if문 에서 charArr[i] chararry[i] -'A'; 하는 이유 ?

3. void SetMatrixChar 에서 boolean findNullFlag = true; 하고 break 하면 어떻게 되나요 ?

3. void SetMatrixChar 에서 else if chararray[i] == '\0' 에서 \0' 는 소스에서 어떤 역할을 수행하나요 ?

4. void SetMatrixChar(const*char chararray) 역할을 잘 모르겠습니다

#include
#define A { 0x18,0x24,0x24,0x42,0x7E,0x42,0x42,0x42 } 

#define B { 0x7C,0x42,0x42,0x7C,0x42,0x42,0x42,0x7C }

#define C { 0x18,0x24,0x40,0x40,0x40,0x40,0x24,0x18 }

#define D { 0x78,0x44,0x42,0x42,0x42,0x42,0x44,0x78 }

#define E { 0x7E,0x40,0x40,0x7E,0x40,0x40,0x40,0x7E }

#define F { 0x7E,0x40,0x40,0x7C,0x40,0x40,0x40,0x40 }

#define G { 0x18,0x24,0x40,0x40,0x46,0x42,0x24,0x18 }

#define H { 0x42,0x42,0x42,0x7E,0x42,0x42,0x42,0x42 }

#define I { 0x08,0x08,0x08,0x08,0x08,0x08,0x08,0x08 }

#define J { 0x02,0x02,0x02,0x02,0x02,0x42,0x24,0x18 }

#define K { 0x44,0x48,0x50,0x60,0x50,0x48,0x44,0x42 }

#define L { 0x40,0x40,0x40,0x40,0x40,0x40,0x40,0x7E }

#define M { 0x66,0x5A,0x5A,0x5A,0x5A,0x5A,0x42,0x42 }

#define N { 0x42,0x62,0x52,0x52,0x4A,0x4A,0x46,0x42 }

#define O { 0x18,0x24,0x42,0x42,0x42,0x42,0x24,0x18 }

#define P { 0x7C,0x42,0x42,0x42,0x7C,0x40,0x40,0x40 }

#define Q { 0x18,0x24,0x42,0x42,0x42,0x4E,0x26,0x1A }

#define R { 0x7C,0x42,0x42,0x42,0x7C,0x48,0x44,0x42 }

#define S { 0x3C,0x42,0x40,0x20,0x1C,0x02,0x02,0x3C }

#define T { 0x3E,0x08,0x08,0x08,0x08,0x08,0x08,0x08 }

#define U { 0x42,0x42,0x42,0x42,0x42,0x42,0x24,0x18 }

#define V { 0x42,0x42,0x42,0x42,0x42,0x42,0x24,0x18 }

#define W { 0x44,0x44,0x54,0x54,0x54,0x28,0x28,0x28 }

#define X { 0x42,0x24,0x18,0x18,0x18,0x24,0x42,0x42 }

#define Y { 0x44,0x44,0x44,0x28,0x10,0x10,0x10,0x10 } 

#define Z { 0x7E,0x02,0x04,0x08,0x10,0x20,0x40,0x7E }

#define SPACE { 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 }

#define SPACE_INDEX 26
#define MAX_CHAR   20   
int cols[8] = {0,1,2,3,4,5,6,7};      //MATRIX 모듈에서 cols과 연결된 핀입니다.
int rows[8] = {14,15,16,17,18,19,20,21}; //MATRIX 모듈에서 rows와 연결된 핀입니다.
const byte font[SPACE_INDEX+1][8] = {  A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,SPACE };

byte charArr[MAX_CHAR+1];
int gSaveCharLen;  
int gCurCharIndex;
int gCurStartColumnIndex;
int gCurColumnIndex;
int gColumnCounter;
int gDisplayInterval = 5000;
int gDisplayIntervalCounter;
byte curCharData[8]; //

void SetMatrixChar(const char* chararray ) {  //표시할 문자를 저장하는 함수로 A~Z까지 비교하여 문자가 같으면 버퍼에 저장하는 함수
    boolean findNullFlag = false;

    for(int i = 0; i <  MAX_CHAR ; i++ )   
    {   if ( ('A'<= chararray[i]) && ('Z' >= chararray[i]) )   {
      charArr[i] = chararray[i] - 'A';    }   
     
   
    else if ( chararray[i] == '\0' )   {
      gSaveCharLen = i;   
      charArr[i] = SPACE_INDEX;  
      findNullFlag = true;   
      break;   
  
      }  
      else   { 
        charArr[i] = SPACE_INDEX; 
    
        }
  }
 if (!findNullFlag) {            
  gSaveCharLen = MAX_CHAR;       

  charArr[MAX_CHAR] = SPACE_INDEX; 
  }
   }

  
void setup(){ 
    for(int i= 0; i< 8 ;i++ )  
    {
     pinMode(cols[i], OUTPUT); 
     digitalWrite(cols[i], HIGH); 
     pinMode(rows[i], OUTPUT);
     digitalWrite(rows[i], LOW);  
    }
 

    gCurColumnIndex = 0;  
   
    }

    void MatrixPerodicDisplay(){  
      digitalWrite(rows[gCurColumnIndex], LOW); // previous row off    
      gCurColumnIndex++;    
      if ( gCurColumnIndex >= 8 )
      gCurColumnIndex = 0; 
    
    for (int i = 0; i < 8 ; i++ )    
    {  if ( curCharData[gCurColumnIndex] & (0x80 >> i) )  {  
      digitalWrite(cols[i], LOW);  } 
      else  {  
        digitalWrite(cols[i], HIGH); 
        }    
        }
        digitalWrite(rows[gCurColumnIndex], HIGH); // previous row ON   
    }
  

void SlideChange() { 
  gDisplayIntervalCounter++;        
  if ( gDisplayIntervalCounter < gDisplayInterval)          
   return;       //조건만족시함수void SlideChange() 함수종료 ? or gDisplayIntervalCounter++;로 돌아감 (?)

         
  gDisplayIntervalCounter = 0;         
  gCurStartColumnIndex++;              
  if ( gCurStartColumnIndex >= 8 )      
  {            
    gCurStartColumnIndex = 0;                 
    gCurCharIndex++;                         
    if ( gCurCharIndex >= gSaveCharLen )      
    {
     gCurCharIndex = 0;                      
    }        
   }       
  for(int i = 0; i < 8 ; i++)        
  {            curCharData[i] = (font[charArr[gCurCharIndex]][i] << gCurStartColumnIndex) | \                
  (font[charArr[gCurCharIndex + 1]][i] >> (8 - gCurStartColumnIndex));                  
  }
 

}

void loop()
{ 
    MatrixPerodicDisplay(); 
    SlideChange();           
    SetMatrixChar("HELLO  HELLO");  
   
}