UART communication(Universal Asynchronous Receiver/Transmitter)
The UART communication protocol is composed of three electric wire
Tx == transmission
Rx == Reception
GND == reference 0V
the alimentation of Tx and Rx pins is +or- equal at +12v, -12v.
For using the UART library you must install the librs232 on Angstrom
CMD: opkg install librs232
the serial link allows communication with the dsPIC. for example if
you want to move the robot, the Beagelboard send a tram towards of
dsPIC. see Communication protocol in part "5) Study" for more
information
Description of use to librs232:
initialisation
// declare and initialize the structure at null
struct rs232_port_t *p = NULL;
// initialize the serial link
p = rs232_init();
// choose the port of communication
rs232_set_device(p, "/dev/ttyS2");
// open the serial link
ret = rs232_open(p);
speed
// choose the speed
rs232_set_baud(p, RS232_BAUD_115200);
send
// write the character
ret = rs232_write_timeout(p, data, 1, &bytes, 1000);
receive
// read the character
ret = rs232_read_timeout(p, data, 1, &bytes, 1000);
close
// close the serial link
rs232_end(p);
please look the example of constructor at next address:
https://github.com/ynezz/librs232/blob/master/src/rs232_test.c
or
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#include "stdio.h"
#include "stdlib.h"
#include "termios.h"
#include "fcntl.h"
void raw_mode (fd, old_term)
int fd;
struct termios *old_term;
{
struct termios term;
tcgetattr(fd, &term);
/* Sauve l’ancienne config dans le paramètre */
tcgetattr(fd, old_term);
/* mode RAW, pas de mode canonique, pas d’echo */
term.c_iflag = IGNBRK;
term.c_lflag = 0;
term.c_oflag = 0;
/* Controle de flux hardware RTS/CTS)
* term.c_cflag |= (CREAD | CRTSCTS);
* 1 caractère suffit */
term.c_cc[VMIN] = 1;
/* Donnée disponible immédiatement */
term.c_cc[VTIME] = 0;
/* Inhibe le controle de flux XON/XOFF */
term.c_iflag &= ~(IXON|IXOFF|IXANY);
/* 8 bits de données, pas de parité */
term.c_cflag &= ~(PARENB | CSIZE);
term.c_cflag |= CS8;
/* Gestion des signaux modem */
term.c_cflag &= ~CLOCAL;
tcsetattr(fd, TCSANOW, &term);
}
main (int ac, char **av)
{
int fd;
struct termios tty, old;
/* Ouverture du device */
if ((fd = open (av[1], O_RDWR)) < 0) {
perror (av[1]);
exit (1);
}
/* Lecture des paramètres */
tcgetattr(fd, &tty);
tcgetattr(fd, &old);
/* On passe la vitesse à 0 ==> hangup */
cfsetospeed(&tty, B0);
cfsetispeed(&tty, B0);
/* On applique le nouveau paramètrage pendant 1s */
tcsetattr(fd, TCSANOW, &tty);
sleep(1);
write(fd, "Mras2an", sizeof(char) * 15);
sleep(1);
/* On revient à l’ancien et on quitte */
tcsetattr(fd, TCSANOW, &old);
close (fd);
}
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Sujet: UART
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