+/*
+ * setSerialSignal v0.1 9/13/01
+ * www.embeddedlinuxinterfacing.com
+ *
+ *
+ * The original location of this source is
+ * http://www.embeddedlinuxinterfacing.com/chapters/06/setSerialSignal.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+/* setSerialSignal
+ * setSerialSignal sets the DTR and RTS serial port control signals.
+ * This program queries the serial port status then sets or clears
+ * the DTR or RTS bits based on user supplied command line setting.
+ *
+ * setSerialSignal clears the HUPCL bit. With the HUPCL bit set,
+ * when you close the serial port, the Linux serial port driver
+ * will drop DTR (assertion level 1, negative RS-232 voltage). By
+ * clearing the HUPCL bit, the serial port driver leaves the
+ * assertion level of DTR alone when the port is closed.
+ */
+
+/*
+gcc -o setSerialSignal setSerialSignal.c
+*/
+
+
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <termios.h>
+
+/* we need a termios structure to clear the HUPCL bit */
+struct termios tio;
+
+int main(int argc, char *argv[])
+{
+ int fd;
+ int status;
+
+ if (argc != 4)
+ {
+ printf("Usage: setSerialSignal port DTR RTS\n");
+ printf("Usage: setSerialSignal /dev/ttyS0|/dev/ttyS1 0|1 0|1\n");
+ exit( 1 );
+ }
+
+ if ((fd = open(argv[1],O_RDWR)) < 0)
+ {
+ printf("Couldn't open %s\n",argv[1]);
+ exit(1);
+ }
+ tcgetattr(fd, &tio); /* get the termio information */
+ tio.c_cflag &= ~HUPCL; /* clear the HUPCL bit */
+ tcsetattr(fd, TCSANOW, &tio); /* set the termio information */
+
+ ioctl(fd, TIOCMGET, &status); /* get the serial port status */
+
+ if ( argv[2][0] == '1' ) /* set the DTR line */
+ status &= ~TIOCM_DTR;
+ else
+ status |= TIOCM_DTR;
+
+ if ( argv[3][0] == '1' ) /* set the RTS line */
+ status &= ~TIOCM_RTS;
+ else
+ status |= TIOCM_RTS;
+
+ ioctl(fd, TIOCMSET, &status); /* set the serial port status */
+
+ close(fd); /* close the device file */
+}
+