Hi.

Thanks to NERDVANA and soonix and afoken. With respect to access to the RS232 serial, the module I am accessing is an OBD2 automotive module with a USB to serial chip embedded within a plastic sealed module. The handskaking on the serial port is switched off ("none" as indicated with the serial initialisation). Also, the initialisation also seems to suggest a buffering of 256 bytes in both directions.

I have tried changing the size of the write (shorted and longer) but the issue still follows how the data is written to the sub Serial_TrxRcv($parameter). I have a "yucky" work around where I avoid taking the $ccmd (command) directly from the hash, but copy to a $newcmd variable in a very specific way. This is in the following code presentation.

sub ProcessPIDs {
    
    # print "Inside ProcessPIDs \n";

    # Process the input arguments
    my ( $nickname, $ref_nicknametocommand ) = @_;
    my %InSubNickNameToCommand = %{$ref_nicknametocommand};   # De-ref
+rence the reference to an hash
    my $ccmd;
    
    $ccmd = $InSubNickNameToCommand{ $nickname };             # need E
+RROR checking here  !!!!!!
    
    my $newcmd ;
    if ($ccmd eq '0101') {
       $newcmd = '0101';
    } elsif ($ccmd eq '0103') {
       $newcmd = '0103';
    } elsif ($ccmd eq '0104') {
       $newcmd = '0104';
    } elsif ($ccmd eq '0105') {
       $newcmd = '0105';
    } elsif ($ccmd eq '0106') {
       $newcmd = '0106';
    } elsif ($ccmd eq '0107') {
       $newcmd = '0107';
    } elsif ($ccmd eq '010c') {
       $newcmd = '010c';
    } elsif ($ccmd eq '010d') {
       $newcmd = '010d';
    } elsif ($ccmd eq '010e') {
       $newcmd = '010e';
    } elsif ($ccmd eq '010f') {
       $newcmd = '010f';
    } elsif ($ccmd eq '0110') {
       $newcmd = '0110';
    } elsif ($ccmd eq '0111') {
       $newcmd = '0111';
    } elsif ($ccmd eq '0113') {
       $newcmd = '0113';
    } elsif ($ccmd eq '0114') {
       $newcmd = '0114';
    } elsif ($ccmd eq '0115') {
       $newcmd = '0115';
    } elsif ($ccmd eq '011c') {
       $newcmd = '011c';
    } elsif ($ccmd eq '0121') {
       $newcmd = '0121';
    } elsif ($ccmd eq '012e') {
       $newcmd = '012e';
    } elsif ($ccmd eq '012f') {
       $newcmd = '012f';
    } elsif ($ccmd eq '013c') {
       $newcmd = '013c';
    } elsif ($ccmd eq '0142') {
       $newcmd = '0142';
    } elsif ($ccmd eq '0143') {
       $newcmd = '0143';
    } elsif ($ccmd eq '0144') {
       $newcmd = '0144';
    } elsif ($ccmd eq '0145') {
       $newcmd = '0145';
    } elsif ($ccmd eq '0149') {
       $newcmd = '0149';
    } elsif ($ccmd eq '014a') {
       $newcmd = '014a';
    } elsif ($ccmd eq '014c') {
       $newcmd = '014c';
    } else {
            print "Warning; failed to match $ccmd\n";
            die "AMEN !\n";
    }
    
    # my $newcmd = $ccmd;    # this does not work
    print "\$ccmd; $ccmd ".length($ccmd). " \$newcmd; $newcmd ".length
+($newcmd)."\n";

    my $response = Serial_TrxRcv($newcmd);
    my $result;

        .... etc ...
[download]

As indicated in the code above, I could not just copy with "my $newcmd = $ccmd" but had to involve an if statement. In this circumstance the $newcmd can be passed to the sub without the buffer error occurring.

If the $newcmd is copied from a constant in the program then it works.

It's hard to known if the issue is from a very fine timing problem with the serial port treatment or related to how perl reads from a simple scaler embedded with a hash. Please consider issues ?

Regards JC....