First an app for testing the serial output stuff:

#!/usr/bin/perl
#
# $Id: test-serial.pl,v 1.1 2005/09/10 10:39:51 dale Exp $

# Dale Chayes 
# Instrument Lab
# Lamont-Doherty Earth Observatory of Columbia University
#
# Created September 9, 2005
#
# This is intentend as a rapid prototype to figure out what the exact
# serial port parameters for output to the Terascan/WDS.
#
# $Log: test-serial.pl,v $
# Revision 1.1  2005/09/10 10:39:51  dale
# Rapid prototype for configuring serial output from Perl
#
#

use Device::SerialPort;         # for the serial port, available from CPAN
                        # on a Windows box you would use Win32::SerialPort
                       # http://members.aol.com/Bbirthisel/SerialPort.html
# NOTE:
#  1) Paste a more or less correct string in here for testing
#  2) It's possible that the $IN part of the INHDT string will
#     not be acceptable to the WDS/Terascan, it may be expecting
#     $HDHDT instead.
#
#  3) It is very possible that the WDS is not looking at the checksum
#     in which case you can simply change it. The "$" (dollar sign)
#     is likely to be required as part of the NMEA spec.
#
#  4) the WDS is probably looking for a carriage return and a line feed
#     at the end off each line so you may hav eto experiment with 
#     end of line characters.

$OutputString="\$INHDT,150.7,T*26\n";
$PortName="/dev/ttyS1";                 # could be S0 (for built in)

$lockfile = "/tmp/serial_test.lck";
# Create the "port object"

#$PortObj = new Device::SerialPort ($PortName, $quiet, $lockfile)
$PortObj = new Device::SerialPort ($PortName)
       || die "Can't open $PortName: $!\n";


# @handshake_opts = $PortObj->handshake;
# print "The handshake options are: ", @handshake_opts ;


# Configure the serial port
$PortObj->baudrate(4800);
$PortObj->parity("none");       # or "odd" or "even"
$PortObj->databits(7);
$PortObj->stopbits(1);    
$PortObj->handshake("none");    # or "xoff" or "rts" try "man stty"
# $PortObj->stty_ocrlf;         # does not see to work
                                # probably carriage return and linefeed



$x=0;

while ($x < 10) {
    
    $count_out = $PortObj->write($OutputString);
    printf("Wrote (%d)\t%s", $x, $OutputString);
    sleep(1);
    $x=$x+1;

}

$PortObj->close || warn "close failed";
undef $PortObj;                 # returns memory (who cares?)

printf("That's all folks\n");