I am communicating with equipment on a USB COM port using USB-RS485 serial port adapter using Win32::SerialPort A CMD message of six bytes is sent to Equipment, which responds with ACK message.

However, I have trouble reading the ACK messsage returned from Equipment from the COM port. I have used  $PortObj->input; $PortObj->lookfor();  $PortObj->read() to retrieve the string from COM port, but it does not show up.

Port characteristics are: Datarate = 115200 bps, 1 start bit, 8 databits, 1 stop bit, odd parity. 1 Byte = 11 bits. Each 11-bit byte has duration 11/115200 = 95.49 us. Timing is approx: 0.5msec: CMD message six bytes duration, 2 msec later ACK message, 2msec ACK message duration. 20 msec between successive CMD messages.

Nearly any combinations of values on  $PortObj->read_interval(), $PortObj->read_char_time(), $PortObj->read_const_time() times, but it does not read the the COM port. I tried these methods and they do not read COM port, and gives in Error messages,

 
: CMD  01 61 00 00 01 61
Second Read attempted before First is done at serial_io.pl line 20.
Use of uninitialized value $got in numeric ne (!=) at C:/appl/strawber
+ry64/perl/site/lib/Win32/SerialPort.pm line 1560.
: ACK
[download]

#!C:\appl\strawberry64\perl\bin
use strict;
use warnings 'all';
use Win32::SerialPort;
use Time::HiRes qw (time sleep);
use Data::Dumper;
my $PortObj_r = &com_port_initialize() ;
my @byte = (0x01, 0x61, 0x00, 0x00, 0x01, 0x61 );
my $str     = ": CMD ";
foreach ( @byte ) { $str .= sprintf(" %02X", $_)};
my $string_in; my $count_in;

while ()
{      
    my $PortObj_r = &get_PortObj;  # Call Port Obj  #
    my $PortObj   = $$PortObj_r;
    print "$str \n";
    foreach my $num ( @byte ) { $PortObj->transmit_char($num) }

    $string_in = $PortObj->input;             # Error: Line 20 ** #
#    $string_in = $PortObj->lookfor();        # Error: Line 21 ** #
#    ($count_in, $string_in) = $PortObj->read(1); # Error: Line 22 #
    print ": ACK "; print $string_in; print "\n";
    
    sleep( 0.020 );   # 20 millisec between writes
    undef $PortObj;
}  # -----------------------------------------

sub get_PortObj { $PortObj_r; }

# --------------------------------------------------------
# PortObject Definiton
# --------------------------------------------------------
sub com_port_initialize         
{
    my $quiet = 1;   
    $| = 1;          
    my $PortName = "COM10";
    my $PortObj = new Win32::SerialPort ($PortName, $quiet)
         || die "Error: Can't open $PortName: $^E\n";    
    print "> PortName = ",  $PortObj->alias, "\n";

    my $dataRate = 115200;
    my $read_bufferSize = 4096;
    my $write_bufferSize = 4096;
    my $char11_t   = (11/$dataRate) ; # 95.49 us  = 0.095 msec

    my $readChar_t     = 1 ; # in millisec; char11_t 
    my $readConst_t    =  2;        # read_const_time
    my $readInterval_t =  10;
    my $writeCharTime  = 1; 
    my $writeConstTime = 0;
    
    $PortObj->handshake("none");   
    $PortObj->user_msg("ON");
    $PortObj->baudrate($dataRate);
    $PortObj->databits(8);
    $PortObj->parity("odd");
    $PortObj->stopbits(1);
    $PortObj->binary('T');          
    $PortObj->parity_enable('T');  
    $PortObj->debug(0);

    $PortObj->buffers($read_bufferSize, $write_bufferSize);
    $PortObj->read_interval($readInterval_t ); 
    $PortObj->read_char_time($readChar_t );   
    $PortObj->read_const_time($readConst_t);   
    $PortObj->write_char_time($writeCharTime);
    $PortObj->write_const_time($writeConstTime);
    $PortObj->write_settings || undef $PortObj;

    my  $ModemStatus = $PortObj->modemlines;
    if ($ModemStatus & $PortObj->MS_RLSD_ON) { print "> Carrier Detect
+ed"; }
    
    open  OUTFILE, ">portObj.txt"  or 
          die "Error: Cannot open portObj.txt  $!\n";
    print OUTFILE "> PortObj = ", Dumper \\$PortObj; 
    close OUTFILE;
    \$PortObj;      # return reference to $PortObj
}
[download]