can ble central send data to peripheral without connection?

[max]

How reply without connection to advertisement packet

[Petter Myhre]

No, it cannot.

The only thing it can send to the peripheral is a scan request, this can be detected in the application with the BLE_GAP_EVT_SCAN_REQ_REPORT event. It contains the peer address and the RSSI:

typedef struct
{
  int8_t                  rssi;              /**< Received Signal Strength Indication in dBm. */
  ble_gap_addr_t          peer_addr;         /**< Bluetooth address of the peer device. If the peer_addr resolved: @ref ble_gap_addr_t::addr_id_peer is set to 1
                                                  and the address is the device's identity address. */
} ble_gap_evt_scan_req_report_t;