$coupon->setType(Mage_SalesRule_Helper_Coupon::COUPON_TYPE_SPECIFIC_AUTOGENERAT‌​ED)->save();

 // Get the rule id
        $rule = Mage::getModel('salesrule/rule')->load(1);

        // Define a coupon code generator model instance
        // Look at Mage_SalesRule_Model_Coupon_Massgenerator for options
        $generator = Mage::getModel('salesrule/coupon_massgenerator');

        $parameters = array(
            'count'=>1,
            'format'=>'alphanumeric',
            'dash_every_x_characters'=>4,
            'prefix'=>'test',
            'suffix'=>'test2',
            'length'=>12
        );

        if( !empty($parameters['format']) ){
            switch( strtolower($parameters['format']) ){
                case 'alphanumeric':
                case 'alphanum':
                    $generator->setFormat( Mage_SalesRule_Helper_Coupon::COUPON_FORMAT_ALPHANUMERIC );
                    break;
                case 'alphabetical':
                case 'alpha':
                    $generator->setFormat( Mage_SalesRule_Helper_Coupon::COUPON_FORMAT_ALPHABETICAL );
                    break;
                case 'numeric':
                case 'num':
                    $generator->setFormat( Mage_SalesRule_Helper_Coupon::COUPON_FORMAT_NUMERIC );
                    break;
            }
        }

        $generator->setDash( !empty($parameters['dash_every_x_characters'])? (int) $parameters['dash_every_x_characters'] : 0);
        $generator->setLength( !empty($parameters['length'])? (int) $parameters['length'] : 6);
        $generator->setPrefix( !empty($parameters['prefix'])? $parameters['prefix'] : '');
        $generator->setSuffix( !empty($parameters['suffix'])? $parameters['suffix'] : '');

        // Set the generator, and coupon type so it's able to generate
        $rule->setCouponCodeGenerator($generator);
        $rule->setCouponType( Mage_SalesRule_Model_Rule::COUPON_TYPE_AUTO );

        // Get as many coupons as you required
        $count = !empty($parameters['count'])? (int) $parameters['count'] : 1;
        $codes = array();
        for( $i = 0; $i < $count; $i++ ){
            $coupon = $rule->acquireCoupon();
            $coupon->setType(Mage_SalesRule_Helper_Coupon::COUPON_TYPE_SPECIFIC_AUTOGENERATED)->save();
            $code = $coupon->getCode();
            $codes[] = $code;
        }
        return $codes;
    }