Can't get values for multiple checkbox in CodeIgniter

I have the following code in my form to submit multiple checkbox

application/views/form.php

<form action="<?php echo base_url().'admin/addMessage/'.$pd_name; ?>" method= "POST">
<div class="form-group">
    <label><strong>Message Type *</strong></label>
    <input type="text" class="form-control" name="msg_type" id="msg_type" placeholder="Enter Message Type" required>
</div>
<label><strong>Message Bit *</strong></label>
<div class="form-group">
    <div class="checkbox">             
        <table class="table">
        <tbody>
        <tr>
            <td><label>          P-1    &nbsp;&nbsp;</label><input type="checkbox" checked disabled readonly /></td>
            <td><label id="P17"> P-17   &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox"  value="P17"/></td>
            <td><label id="P33"> P-33   &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox" value="P33" /></td>
            <td><label id="P49"> P-49   &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox" value="P49"/></td>
            <td><label id="S65"> S-65   &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox" value="S65" /></td>
            <td><label id="S81"> S-81   &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox"  value="S81" /></td>
            <td><label id="S97"> S-97   &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox" value="S97" /></td>
            <td><label id="S113"> S-113 &nbsp;&nbsp;</label><input name="bitmsg" type="checkbox" value="S113"/></td>
        </tr>
        </tbody>
        </table>
    </div>
</div>
<button type="button" class="btn btn-default" id="reset" data-dismiss="modal">Cancel</button>
<button type="submit" value="submit" class="btn btn-primary"> Add New Message Type</button>
</form>

application/controller/Admin.php

public function addMessage($pdID)
{
    $this->load->helper('form');
    $this->load->library('form_validation');

    $this->form_validation->set_rules('msg_type', 'MessageType', 'required');


    if ($this->form_validation->run() == FALSE)
    {   
        echo '<script>alert("Please Select Valid Message Type"); window.history.back();</script>';
    }
    else
    {
        $this->model_general->set_message($pdID);
    }

}

application/models/Model_general.php

function set_message()
{
    $this->load->helper('url');
    $this->load->helper('form');

    //set default values    
    $dbEntry = array(
        'P17'  => 0,'P33' => 0,'P49' => 0,'S65' => 0,'S81' => 0,'S97' => 0,'S113' => 0
    );

    $postData = $this->input->post();

    foreach ($postData as $key => &$v) {

        if (array_key_exists($key, $dbEntry)) {

            $dbEntry[$key] = 1;
        }
        elseif ($key == 'bitmsg') {

            $dbEntry[$v] = 1;
        }
        else {

            $dbEntry[$key] = $v;
        }
    }

    $this->db->insert('msg_format', $dbEntry);
}

I did select all checkbox.. but $postData only return the last checkbox that i checked. E.g:

$postData return "MsgType1,0,0,0,0,0,0,1" <<= if select all

$postData return "MsgType2,0,0,0,0,0,1,0" <<= if i select all except S-113

Something missing and I couldn't find it.. :/