How to add Additional Data in Payment Additional Data Field

Set additional data/information in payment instance

If you want to add the additional information in payment instance, then

Step1
In the Model file of your created payment

Mage_Payment_Model_Method_[custom_name]

add the below code in

assignData()

function

$this->getInfoInstance()->setAdditionalData([value to set]);

for example

$data['pay'] = 'xxxx';
$this->getInfoInstance()->setAdditionalData(serialize($data));

Step2
In Block folder, create payment info file that extends info block, add the below code in info phtml file

protected $_pay;

public function getPay()
{
     if (is_null($this->_pay)) {
        $this->_convertAdditionalData();
     }
     return $this->_pay;
}

protected function _convertAdditionalData()
{
    $this->_pay= '';

    $data = @unserialize($this->getInfo()->getAdditionalData());        
    if (is_array($data )) {
         $this->_emi = isset($data ['pay']) ? (string) $data ['pay'] : '';
    }
    return $this;
}

Step3
In the payment info phtml file, add the below code to show the additional data added.

<?php  
echo ( if($this->getPay()) ? $this->getPay() : '');  
?>

Now check the

additional_data field

in

sales_flat_order_payment

table for that order, you will find the data that added in table.