Well, I make some modifications into my script and now it is working. I use method with Tied FileHandles and that seems to have no problem with long strings. Below is the script. Next step will be to send continious string of data from one serial port to the different one. I will keep you posted. Robert

#!/usr/bin/perl
use strict;
use warnings;
use Device::SerialPort;

my $PORT = "/dev/ttyO1";
my $Config = "serial.cfg";
my $string  = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20";

my $ob = Device::SerialPort->new($PORT) || die "Can't Open $PORT: $!";

$ob->baudrate(115200) || die "failed setting baudrate";
$ob->parity("none") || die "failed setting parity";
$ob->databits(8) || die "failed setting databits";
$ob->handshake("none") || die "failed setting handshake";
$ob->write_settings || die "no settings";
$| = 1;

$ob->write_settings;
$ob->save("serial.cfg");
$ob = tie (*FH, 'Device::SerialPort', $Config)
       || die "Can't tie: $!\n";             ## TIEHANDLE ##

print FH $string;

close FH || warn "close failed";
undef $ob;
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One more thing: you probably can replace the

  my $ob = Device::SerialPort->new($PORT) || die;
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With just the tie (eschewing the config file):

  my $ob = tie (*FH, 'Device::SerialPort', $PORT) || die;
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Untested though.