sub SerRead {
$ser_dev = "/dev/ttyS3";
$AckOk = "\x06";
$AckErr = "\x15";

	sysopen ( SerialRead, "$ser_dev", O_RD | O_NONBLOCK ) || die "cannot sysopen";  

	$len="";
	while (length($len) == 0){
	       $len = sysread(SerialRead, $buf, 1 );
	}
	if ($buf == $AckOk) {
		print "ACK_OK\n";
	}
	if ($buf == $AckErr) {
		print "ACK_ERR\n";
	}
	
	close SerialRead;

}