Send a break to a serial/rs232 device from the terminal using tcsendbrake termios. I use this on OS X to soft-reset my mbed LPC1768. To compile: gcc -o sendbreak sendbreak.c Don't have gcc installed? I think it comes with xcode.

sendbreak.c

#include <termios.h>
#include <fcntl.h>
#include <stdio.h>
 
int main(int argc,char** argv) {
  if (argc<2) {
    printf("Usage: One parameter, the device to send the "
           "break to. Example: %s /dev/tty.usbmodem622 \n",argv[0]);
  } else {
    int tty_fd = open(argv[1], O_RDWR | O_NONBLOCK);
    tcsendbreak(tty_fd, 0);
  }
}