Упражнение 4. Сериен порт (2)

Разглеждане на сигнал на сериен порт

Задача 1 Създайте програма с безкраен цикъл, която да изпраща една буква към серийния порт. Използвайте специално пригодения кабел и разгледайте осцилограмата на серийни сигнал.

приемане

#include <termios.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
      
#define BAUDRATE B9600
#define MODEMDEVICE "/dev/ttyS0"
       
 int  main()
 {
 
        int fd,c, res, stop = 0;
        struct termios oldtio,newtio;
        char buf[255];
        
        /* open the device to be non-blocking (read will return immediatly) */
        fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);
        if (fd < 0) {perror(MODEMDEVICE); exit(-1);}
        
        fcntl(fd, F_SETFL, 0);
	    fcntl(fd, F_SETFL, FNDELAY);        
        
        
               
        tcgetattr(fd,&oldtio); /* save current port settings */
        /* set new port settings for canonical input processing */
        newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
        newtio.c_iflag = IGNPAR | ICRNL;
        newtio.c_oflag = 0;
        newtio.c_lflag = ICANON;
        
        tcflush(fd, TCIFLUSH);
        
            newtio.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL|IXON);
            newtio.c_cflag &= ~( CRTSCTS );
            newtio.c_oflag &= ~OPOST;
            newtio.c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
            newtio.c_cflag &= ~(CSIZE|PARENB);
            newtio.c_cflag |= CS8;
        
        newtio.c_cc[VMIN]=1;
        newtio.c_cc[VTIME]=0;
        tcsetattr(fd,TCSANOW,&newtio);
         
        /* loop while waiting for input. normally we would do something
           useful here */ 
              
    while ( stop == 0)
	{
         
         usleep(100); 
         fflush (stdout);
         res = read(fd,buf,10);
            // strcat(buf,buf2);
          
            for( c=0;c<res; c=c+1)
            {
              if ( buf[c] == 0xd )  
              printf ("\n");
              else 
              {
		if (buf[c] == 0x61) { printf("oko");stop = 1;}
		printf("%c", (char) buf[c]);
	      }
            
            }
        }
        
        /* restore old port settings */
        tcsetattr(fd,TCSANOW,&oldtio);
 return 0;
 }