RX and TX characteristics in ble_app_uart example

[diode]

I want to transfer some data stored in nRF51822 to another BLE central device. I guess the idea is very similar to "ble_app_uart" example except that I don't need the part interfacing with local hardware UART. The app seems to send out data via notifications. It seems a very silly question, but why do I still need TX characteristics when the data are already in the notification packet?

Also, the documentation indicates "the peer can send data to the device by writing to the RX Characteristic of the service". However, the "on_write" function in "ble_nus.c" actually indicates the handle is of TX characteristic:

static void on_write(ble_nus_t * p_nus, ble_evt_t * p_ble_evt)
{
    ble_gatts_evt_write_t * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;

    if (
        (p_evt_write->handle == p_nus->rx_handles.cccd_handle)
        &&
        (p_evt_write->len == 2)
       )
    {
        if (ble_srv_is_notification_enabled(p_evt_write->data))
        {
            p_nus->is_notification_enabled = true;
        }
        else
        {
            p_nus->is_notification_enabled = false;
        }
    }
    else if (
             (p_evt_write->handle == p_nus->tx_handles.value_handle)
             &&
             (p_nus->data_handler != NULL)
            )
    {
        p_nus->data_handler(p_nus, p_evt_write->data, p_evt_write->len);
    }
    else
    {
        // Do Nothing. This event is not relevant for this service.
    }
}

Why is there such a difference?

[diode]

I misunderstood the concept of notification. The data written to this notification-enabled characteristic will be pushed to the client. Thanks for the clarification.