// DateTime : 2018-04-27 오전 12:16:15
// by Ok-Hyun Park
//=====================================================================//
#include <mega128.h>
#include <delay.h>
//=====================================================================//
char fnd[]={0xC0,0xF9,0xA4,0xB0,0x99,0x92,0x82,0xF8,0x80,0x90,0x88,0x83,0xC6,0xA1,0x86,0x8E}; //애노드
char buf[4]={0};
//
void disp(){
  PORTA=fnd[buf[0]];      PORTB=1; delay_ms(1); PORTB=0;
  PORTA=fnd[buf[1]];      PORTB=2; delay_ms(1); PORTB=0;
  PORTA=fnd[buf[2]]&0x7F; PORTB=4; delay_ms(1); PORTB=0;
  PORTA=fnd[buf[3]];      PORTB=8; delay_ms(1); PORTB=0;
}
//
char KeyScan(void){
  char KeyBuf=0xFF;
  DDRC=0; PORTC=~0;
  DDRC=0x08; PORTC.3=0; delay_us(1); if(!PINC.0)KeyBuf= 1; if(!PINC.1)KeyBuf=2; if(!PINC.2)KeyBuf= 3; DDRC=0; PORTC=~0;
  DDRC=0x10; PORTC.4=0; delay_us(1); if(!PINC.0)KeyBuf= 4; if(!PINC.1)KeyBuf=5; if(!PINC.2)KeyBuf= 6; DDRC=0; PORTC=~0;
  DDRC=0x20; PORTC.5=0; delay_us(1); if(!PINC.0)KeyBuf= 7; if(!PINC.1)KeyBuf=8; if(!PINC.2)KeyBuf= 9; DDRC=0; PORTC=~0;
  DDRC=0x40; PORTC.6=0; delay_us(1); if(!PINC.0)KeyBuf=10; if(!PINC.1)KeyBuf=0; if(!PINC.2)KeyBuf=11; DDRC=0; PORTC=~0;
  return KeyBuf; // Key 없으면 0xFF 리턴
}
//=====================================================================//
void main(void){
    char i,key,old;
    DDRA=0xFF; DDRB=0x0F;
    old=KeyScan();                                // 무한루프 들어가기 전에 키값을 저장해 두고
    while(1){
        key=KeyScan();                            // 키를 입력받아서
        if(old!=key){                             // 저장된 값과 다르면 (새로운 키가 눌렸으면)
            if((key>=0)&&(key<=11)){              // 키값의 범위를 체크하고
                for(i=2;i>=0;i--)buf[i+1]=buf[i]; // 버퍼를 시프트 시킨 후
                buf[0]=key;                       // 버퍼0에 키값을 저장
            }
            old=key; // 현재 키값을 저장
        }
        disp();
    }
}
 
FND 4x3 키 매트릭스 & FND(4자리) 프로테우스 ( 코드비전 & AVRstudio)  
https://www.basic4mcu.com/bbs/board.php?bo_table=gesiyo10&wr_id=191 
이 소스를 수정해서 인터럽트 대신 폴링 방식으로 수정했습니다.