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Old 04-09-2013, 11:40 AM   #1
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Registered: Dec 2012
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Communication failure

hye guys, i have this C code to communicate with external device which i need to send command and retrieve data from it but it's not working although it can be compiled. I'm not really good in C, please help me guys. Thanks in advanced.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <errno.h>
#include <termios.h>

#define FALSE 0
#define TRUE 1

volatile int STOP=FALSE; 
int wait_flag=TRUE;  /* TRUE while no signal received */

void signal_handler_IO (int status);   /* definition of signal handler */

int n;
int fd, res;
int connected;
struct termios termAttr;
struct sigaction saio;
char buf[255];

int main(int argc, char *argv[])
     fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY);
     if (fd == -1)
        perror("open_port: Unable to open /dev/ttyO1\n");

     saio.sa_handler = signal_handler_IO;
     saio.sa_flags = 0;
     saio.sa_restorer = NULL; 

     fcntl(fd, F_SETFL, FNDELAY);
     fcntl(fd, F_SETOWN, getpid());
     fcntl(fd, F_SETFL,  O_ASYNC ); /**<<<<<<------This line made it work.**/

     //baudRate = B115200;          /* Not needed */
     termAttr.c_cflag &= ~PARENB;
     termAttr.c_cflag &= ~CSTOPB;
     termAttr.c_cflag &= ~CSIZE;
     termAttr.c_cflag |= CS8;
     termAttr.c_cflag |= (CLOCAL | CREAD);
     termAttr.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
     termAttr.c_iflag &= ~(IXON | IXOFF | IXANY);
     termAttr.c_oflag &= ~OPOST;
     printf("UART1 configured....\n");

     connected = 1;
     while(connected == 1){
           // some code
            if (wait_flag==FALSE) { 
            res = read(fd,buf,255);
            printf(":%s:%d\n", buf, res);
            if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
            wait_flag = TRUE;      /* wait for new input */



void signal_handler_IO (int status)
     printf("received data from UART.\n");
Old 04-09-2013, 01:04 PM   #2
Registered: Mar 2011
Location: Sutton, MA. USA
Distribution: MINT Debian, Angstrom, SUSE, Ubuntu
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All you said what it didn't work, not what the problem specifically is.

Have you tried using minicom to talk to this port and been successful?

I think if you're 115.2K N81 nothing special, then you don't need to set all the port settings explicitly, just read the attributes, configure the speed, and set the attributes.

Does the port normally send out periodic data? If so then do receive first and verify that you can receive and properly interpret the data. Next send it the most basic command, like a version command or something so you can see the result.

Looks like a binary code. I don't use escape sequences and hex or octal designators in a visible string, what I do instead is declare the data truly as hex. So what I would do instead would be to declare that command as an array of characters or unsigned characters.

static unsigned char myCommand[8] = { 0xf5, 0x01, 0x00, 0x01, 0x03, 0x00, 0x03, 0xf5 };
And then write(2) myCommand to the file descriptor. Also check the result from the call to write(2). Never ignore a library's function return.

if((cnt = write(fd, myCommand, sizeof(myCommand))) != sizeof(myCommand)) {
  // print error, check errno, also use strerror(errno), but print the actual errno
  // check the possible errors that can come from invoking write(2)
Old 04-11-2013, 09:39 AM   #3
Registered: Dec 2009
Location: Germany
Distribution: Whatever fits the task best
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Please post your thread in only one forum. Posting a single thread in the most relevant forum will make it easier for members to help you and will keep the discussion in one place. This thread is being closed because it is a duplicate.

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