Hi thndergnat, I'm using ModBus RTU via a Digi CM-32 NTS. Basically I telnet onto the port and transmit the data over the Telnet line using ASCII characters. Weird enough it works perfectly with positive integers but once I use negative values, it seems to have a lot of problems. @buffor is the buffer I'm using to hold the data and it's a global array. Thanks for the help! Regards, Paul. 
     $buffor[0] = chr($slave_add);
    $buffor[1] = chr($readwrite);
    my $pack_val = unpack("H*",pack("n",$start_add));
    my $tmp1= (substr $pack_val, 0, 2);
    my $tmp2= (substr $pack_val, 2, 2);
    $buffor[2] = chr(hex (substr $pack_val, 0, 2));
    $buffor[3] = chr(hex (substr $pack_val, 2, 2));
    $pack_val = unpack("H*",pack("n",$quantity));
    my $tmp3= (substr $pack_val, 0, 2); #FF
    my $tmp4= (substr $pack_val, 2, 2); #EB
    $buffor[4] = chr(hex (substr $pack_val, 0, 2));
    $buffor[5] = chr(hex (substr $pack_val, 2, 2));
    $buffor[6] = chr(CRC_calc(1));
    $buffor[7] = chr(CRC_calc(0));
    my $tmp5 = CRC_calc(1);
    my $tmp6 = CRC_calc(0);

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In reply to Re^2: Telnet.pm and Negative Values for Modbus by PaulNg
in thread Telnet.pm and Negative Values for Modbus by PaulNg

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