Thanks to Dave Platt for pointing me in the right direction for RTS / DTR
control from a user app.  However, I'm still not able to get it to work.
I'm using the following test code (port open code not shown, purloined from
a Ham Radio application):

int arg, q;

arg = TIOCM_RTS | TIOCM_DTR;
while(TRUE) {
    if ( ioctl(fd, q ? TIOCMBIS : TIOCMBIC, &arg) < 0 ) printf("ioctl
Error\n");
   q = !q;
   sleep(1);

But the lines don't wiggle.  I've also used the TIOCMSET function to try to
wiggle them.  I've looked through serial.c (Redhat Linux 6.2 on PC) and
didn't see anything (like a particular open mode) that would prevent the
calls from working.  Anybody have any ideas how to proceed with debugging?

Thanks, Doug

CLOCAL and TIOCM_DTR interact with the serial driver in ways which are
less than obvious.  The following code should serve your purpose.

--------cut here--------

#include        <termio.h>
#include        <unistd.h>
#include        <errno.h>
#include        <fcntl.h>
#include        <stdarg.h>
#include        <stdio.h>
#include        <string.h>

#define DEV     "/dev/ttyS1"

#define bool    char
#define not     !
#define TRUE    (0 == 0)
#define FALSE   (not TRUE)

static bool     process( ),
                complain( char *, ...);

int
main( )
{

        return (process( )? 0: 1);

static bool
process( )
{
        struct termio   t;
        int             n,
                        a,
                        i;

        int fd = open( DEV, O_RDWR|O_NONBLOCK);
        if (fd < 0)
                return (complain( "cannot open %s (%s)", DEV, strerror( errno)));
        i = ioctl( fd, TCGETA, &t);
        if (i < 0)
                return (complain( "TCGETA failed (%s)", strerror( errno)));
        t.c_cflag |= CLOCAL;
        i = ioctl( fd, TCSETA, &t);
        if (i < 0)
                return (complain( "TCSETA failed (%s)", strerror( errno)));
        for (n=0; n<5; ++n) {
                a = TIOCM_RTS | TIOCM_DTR;
                i = ioctl( fd, TIOCMBIS, &a);
                if (i < 0)
                        return (complain( "TIOCMBIS failed (%s)", strerror( errno)));
                sleep( 1);
                a = TIOCM_RTS | TIOCM_DTR;
                i = ioctl( fd, TIOCMBIC, &a);
                if (i < 0)
                        return (complain( "TIOCMBIC failed (%s)", strerror( errno)));
                sleep( 1);
        }
        return (TRUE);

static bool
complain( char *mesg, ...)
{
        va_list ap;

        va_start( ap, mesg);
        vfprintf( stderr, mesg, ap);
        fprintf( stderr, "\n");
        return (FALSE);

--------