Thread: Wirte and read serial port

Originally Posted by jimblumberg

So what is fd in the following snippet?

Code:

 mainfd = open_port();
 

 write(fd,"\xF5\x01\x00\x01\x03\x00\x03\xF5",8);

The port file descriptor looks to be be mainfd, not fd.

Jim

OMG! what a stupid mistakes i made! thanks for pointing it out jimblumberg! ^^.

Another prob is, suppose i get this output from the device "\0xf5\0x01\0x00\0x00\0x00\0x00\0x01\0xf5" but unfortunately not. Here what i get: Got �.

Please repost your current code.

Jim

Originally Posted by stahta01

Did you miss seeing this post; because the question it raises needs answered!

Tim S.

yea i was just replying them both at the same time.^^

Originally Posted by jimblumberg

Please repost your current code.

Jim

Here it is

Code:

 #include <stdio.h>   /* Standard input/output definitions */
 #include <string.h>  /* String function definitions */
 #include <unistd.h>  /* UNIX standard function definitions */
 #include <fcntl.h>   /* File control definitions */
 #include <errno.h>   /* Error number definitions */
 #include <termios.h> /* POSIX terminal control definitions */

 /*
  * 'open_port()' - Open serial port 1.
  *
  * Returns the file descriptor on success or -1 on error.
  */

 int open_port(void)
 {
   int fd;                                   /* File descriptor for the port */

   fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY);

   if (fd < 0) {                                              /* Could not open the port */
     fprintf(stderr, "open_port: Unable to open /dev/ttyUSB0 - %s\n",
             strerror(errno));
   }

   return (fd);
 }

void main()
{
 int mainfd=0,fd;                                            /* File descriptor */
 char chout, result, cnt;
 struct termios options;
   
 mainfd = open_port();

 fcntl(mainfd, F_SETFL, FNDELAY);                  /* Configure port reading */
                                     /* Get the current options for the port */
 tcgetattr(mainfd, &options);
 cfsetispeed(&options, B19200);                 /* Set the baud rates to 19200 */
 cfsetospeed(&options, B19200);
    
                                   /* Enable the receiver and set local mode */
 options.c_cflag |= (CLOCAL | CREAD);
 options.c_cflag &= ~PARENB; /* Mask the character size to 8 bits, no parity */
 options.c_cflag &= ~CSTOPB;
 options.c_cflag &= ~CSIZE;
 options.c_cflag |=  CS8;                              /* Select 8 data bits */
 options.c_cflag &= ~CRTSCTS;               /* Disable hardware flow control */  
 
                                 /* Enable data to be processed as raw input */
 options.c_lflag &= ~(ICANON | ECHO | ISIG);
       
                                        /* Set the new options for the port */
 tcsetattr(mainfd, TCSANOW, &options);

 result = tcsetattr(mainfd, TCSANOW, &options);
 if ( result == -1 ) { perror("error: tcsetattr"); }
 if ( result != 0 ) { fprintf(stderr,"error in tcsetattr, result = %d\n", result); }

 result = write(mainfd,"\xF5\x01\x00\x01\x03\x00\x03\xF5",8);
 if ( result == -1 ) { perror("error: write"); }
 if ( result != 8 ) { fprintf(stderr,"error in write, result = %d\n", result); }
  
 usleep(5000000);      /* wait for 5 second*/
 
 result = read(mainfd, &chout, sizeof(chout));          /* Read character from ABU (Auto buffering Unit) */
 if ( result == -1 ) { perror("error: read"); }
 if ( result != 1 ) { fprintf(stderr,"error in read, result = %d\n", result); }
   
   if (chout != 0)
      printf("Got %c.\n", chout);

   chout=0;
   
 
                                                    /* Close the serial port */
  close(mainfd);
 }

Originally Posted by Salem

Code:

$ gcc -Wall foo.c
foo.c:29:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
foo.c: In function ‘main’:
foo.c:57:7: warning: ‘fd’ is used uninitialized in this function [-Wuninitialized]

Having learnt a lesson, turn on as many warnings as you can.

> Another prob is, suppose i get this output from the device "\0xf5\0x01\0x00\0x00\0x00\0x00\0x01\0xf5" but unfortunately not. Here what i get: Got �.
You need to do things like
printf("%02x\n", ch );

Printing binary data with %c will display random glyphs.

You also need to read in multiple chars, not just one.

I tried to use this "printf("%02x\n", ch );" instead of %c but no data display. i only loop it once first, just to try.

How can i display the output in a new file?

Another prob is, suppose i get this output from the device "\0xf5\0x01\0x00\0x00\0x00\0x00\0x01\0xf5" but unfortunately not. Here what i get: Got �.

Your only reading a single signed character, not a string. Also 0xF5 is outside the size that can be held in a signed character, you should be using an unsigned char not a char.

If you want to read more than this single character I recommend a loop.

Jim

Originally Posted by jimblumberg

Your only reading a single signed character, not a string. Also 0xF5 is outside the size that can be held in a signed character, you should be using an unsigned char not a char.

If you want to read more than this single character I recommend a loop.

Jim

u mean like looping while storing them into an unsigned char array? hurm, my C prog not really good, mind giving me an example?

u mean like looping while storing them into an unsigned char array?

Yep. But you can start by receiving and printing each character as you receive it.

urm, my C prog not really good, mind giving me an example?

You've already done harder, give it a try and if you have problems post your new code and ask specific questions.

Jim

Why are you using an array for the return values? A single value is all you need. And it should not be a char or unsigned char. You would be better off with an int.

Code:

result[i] = read(mainfd, &chout[i], sizeof(chout));          /* Read character from ABU (Auto buffering Unit) */
 if ( result[i] == -1 ) { perror("error: read"); }

Jim

Originally Posted by jimblumberg

Why are you using an array for the return values? A single value is all you need. And it should not be a char or unsigned char. You would be better off with an int.

Code:

result[i] = read(mainfd, &chout[i], sizeof(chout));          /* Read character from ABU (Auto buffering Unit) */
 if ( result[i] == -1 ) { perror("error: read"); }

Jim

Hello, i got a problem now, i need to receive data more than 8 byte which is 111 byte and i tried to loop it 111 times the same thing i did to receive the 111 byte data but i did not receive the correct data. I've uploaded a picture of the 111 byte data which i get by using cutecom software.



Really need help on this part.