Hi. Thanks for the help. I am rid of the warning. In the same way as before, the next 3 sections give my module's code, my test routine and console output

 
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Serial.pm

use Win32::SerialPort;
my $port;

package Serial;

# The following 2 lines I suspect are the lines that make a package in
+to a module
# Also, they seem to make it a member of a class Exporter.
require Exporter;
@ISA = qw( Exporter );  # This module "is a" Exporter class member

#Now declare what we permit to be visible within the module.
@EXPORT = qw( &Serial_Init &Serial_TrxRcv &Serial_Close);

use Time::HiRes qw(usleep);

# ############ subroutine Serial_Init ################################
+###################

sub Serial_Init {

    my $port_name = 'COM5';
    #my $config_file = 'setup.cfg';    # use this to configure from th
+e file

    $port = new Win32::SerialPort( $port_name ) 
                    ||  die "Unable to open: $^E\n";    # $^E EXTENDED
+_OS_ERROR
                                             
    #$port = new Win32::SerialPort($port_name, $config_file) || die "U
+nable to open: $^E\n";

    $port->handshake('none');     # none dtr rts xoff
    $port->baudrate(38400);       # 19200 57600 1200 9600 115200 4800 
+600 2400 300 38400
    $port->parity('none');        # space none odd even mark
    #$port->parity_enable(1);       #      for any parity except "none
+"
    $port->databits(8);           # options 7 8
    $port->stopbits(1);           # options 2 1
    $port->buffers(256, 256);
    $port->read_interval(0);      #RI
    $port->read_const_time(20);   #RC
    $port->write_char_time(1);    #WM
    $port->write_const_time(100); #WC

    print "Write settings;  ";

    $port->write_settings || undef $port;
    # A report out to the console
    my $baud   = $port->baudrate;
    my $parity = $port->parity;
    my $data   = $port->databits;
    my $stop   = $port->stopbits;
    my $hshake = $port->handshake;

    print "B = $baud, D = $data, S = $stop, P = $parity, H = $hshake\n
+\n";
            
    # use the below to save the current configuration
    # if ( $port ) { $port->save('setup.cfg') ; print "Serial Port OK 
+\n" };

    # pack: used for assembling binary stuff
    # my $status = pack('H2' * 6, 'ca', '00', '01', '00', '00', 'fe');

    #$port->write("ati\x0D\x0A");      # carriage return and line feed
+:  no different
    #$port->write("ate0"."\r");    

    #print "test 01\n";
    #usleep 0;
    #print "test 02\n";
    
}

# ############## subroutine Serial_TrxRcv ###############
sub Serial_TrxRcv {
    
    my ($cmd) = @_;
    my $response = "";
    
    #print "cmd; $cmd\n";
    
    $port->write($cmd."\r");
    my $loop = 1;
    while( $loop ) {
        usleep(200000);         # 0.2 of a second
        my $partial_resp;
        $partial_resp = $port->input;
        chomp $partial_resp;    
        $response = $response.$partial_resp;
       
        # print $response;
        
        #my $responseHex = unpack ('H*', $response);
        #print $responseHex."\n";
         
        my $last = substr ( $response, -1 );    # get the last charact
+er
        if ($last eq ">") { $loop = 0; 
                             $response = substr( $response, 0, -1);   
+  # -1 removes the ">";
                             chomp $response;
                             next; 
                          }
        print ".";
    }
    
    return $response;    
}

# ############## subroutine Serial_Close #################
sub Serial_Close {
    $port->close();
}

# ############## Execute when module exits  ##############
END {
  undef $port; # free it before global destruction runs
}

1;

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[download]

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test_Serialpm.pl

#!usr/bin/perl

use strict;
use warnings;


use lib '.';      # The Serial.pm is in the current folder

use Serial;       # use a "1 off type of macro expansion" of the Seria
+l module
#use Serial 'Serial_Init';

Serial_Init();    # Initialise the interface

my $response = Serial_TrxRcv("at dp");   # Transmit "AT Diplay Protoco
+l" and get a response

print "Response is; $response\n";
print "Response num char; ".length($response)."\n";

#Serial_Close();    # This approached removed the closing error wrt $p
+ort
                    # now is not required due to END code added to mod
+ule

----------------------------------------------------------------
[download]

 
-----------------------------------------------------------------
Console output for a simple test;

Write settings;  B = 38400, D = 8, S = 1, P = none, H = none

Response is; at dp
AUTO, SAE J1850 PWM

Response num char; 27
-----------------------------------------------------------------
[download]

The approach of another subroutine "Serial_Close" seems like a work around, but similar to Corion's suggestion.

Other key changes with my initial presentation are removal (from Serial.pm) of warnings, strict and "#!usr/bin/perl" lines. Also the "my" was removed from the @ISA and @EXPORT global arrays. This permitted shorter names in test_Serialpm.pl.

Regards JC.....