How to read RS232 ?

[Altera_Forum]

Hello all, 

 I have problem with UART, when i want to read serial data (hex byte message - something like bytes: 02,05,01,02,05 after this 10ms space and 03,05,xx,yy,zz etc.).    I have development kit DK-DSP-EP2S60 and when i connect the board, which send me bytes to the NIOS2 design with uart and in uClinux i use:   fd = open(S0_232, O_RDWR | O_NDELAY | O_NONBLOCK );  fd = open(S0_232, O_RDONLY | O_NOCTTY | O_NDELAY );   and when the program perform this command, the data from RxD RS232 are sended to the output TxD. I dont understand why ? (why it create loopback on RS232)   How is possible to read data from RS232 without loopback ? (how to set RS232 for reading only ?)   Thank you very much.   Jan Naceradsky, Czech Republic

[Altera_Forum]

I forgot: 

SO_232 is device "/dev/ttyS0"  # define S0_232 "/dev/ttyS0"   Jan Naceradsky

[Altera_Forum]

Because the linux driver will be assuming you want tty semantics. 

You need to change the tty mode - see 'man termios' (at a guess).

[Altera_Forum]

Thank you. 

 I finally solved it with my collegue which advice me to add command   stty -F /dev/ttyS3 sane -echo -icanon   to rc file. This command stop the echo of input characters.  And after open command in program i use:  void init_rs232(void)  { struct termios options;    fd = open(S0_232, O_RDWR | O_NOCTTY | O_NDELAY ); if (fd > 0)  { fcntl(fd, F_SETFL, O_NONBLOCK); tcgetattr(fd, &options); options.c_cflag |= (CLOCAL | CREAD | CS8 ); options.c_cc[VMIN] = 1; options.c_cc[VTIME] = 0; options.c_lflag = FLUSHO; tcsetattr(fd, TCSANOW, &options);  printf("Init RS232 OK.\n");  } }   and now it works well.    Jan Naceradsky

[Altera_Forum]

The 'stty' comand probably does nothing useful - I'm not even sure the values persist once the device is closed. 

You are already disabling echo and icanon when you set c_lflag.

[Altera_Forum]

Yes, you are right, i cancel stty command in linux and use  

--------------------------------------------------- options.c_lflag &= ~(ICANON | ECHO | ISIG );   in open function:    fd = open(S0_232, O_RDWR | O_NOCTTY | O_NDELAY );  // fd = open(S0_232, O_RDWR); // | O_NOCTTY | O_NDELAY );  if (fd > 0)   {    fcntl(fd, F_SETFL, FNDELAY);   tcgetattr(fd, &options);  options.c_cflag |= (CLOCAL | CREAD );  options.c_cflag &= ~PARENB; // set no parity, stop bits, data bits  options.c_cflag &= ~CSTOPB;  options.c_cflag &= ~CSIZE;  options.c_cflag |= CS8;   options.c_cc[VMIN] = 1;  options.c_cc[VTIME] = 0;  options.c_lflag &= ~(ICANON | ECHO | ISIG );  tcsetattr(fd, TCSANOW, &options);   }     But when i read hex message (from PC to Altera NIOS2 system) 16,11,01,00,00,00,00,80,00,7B   the linux read  16,01,00,00,00,00,80,00,7B and the second byte doesn't receive .... i read the termios on: http://slackware.osuosl.org/slackware-3.3/docs/mini/serial-port-programming   and they say that 0x11 is DC1 which mean VSTART for XON and XOFF and i am not able to disable this software flow control.   When i use setting options.c_cflag &= ~(IXON | IXOFF | IXANY); // no flow control   or   options.c_cflag &= ~CRTSCTS;    it doesnt work. Read again:16,01,00,00,00,00,80,00,7B (and the 0x11 is missing).   Do you have somebody program, which can read EVERY characters (hex - 00-FF) without any control meanings ?   Is possible to disable control characters in options.c_cc[xxx] ?   I retype  options.c_cc[VSTART] = 0xFE;   and the message is read ok, but echo was set ... why ?   Where is error ?     Jan, Czech Republic

[Altera_Forum]

Hi all, 

is anyone who can solve this problem ?    Jan

[Altera_Forum]

Are you actually certain the PC is sending the 0x11 byte ?