https://devzone.nordicsemi.com/f/nordic-q-a/66501/ble-characteristics-write-data-issueHi, I want to write 510 bytes of data to my BLE Characteristics, so I set parameters ble_gatts_attr_t max_len as 510 and its variable length attribute. Also I set NRF_SDH_BLE_GATT_MAX_MTU_SIZE as 512. I observed below things: - When I send data lengthen-USTelligent Community 13Wed, 30 Sep 2020 09:56:40 GMThttps://devzone.nordicsemi.com/thread/272224?ContentTypeID=1Wed, 30 Sep 2020 09:56:40 GMT137ad170-7792-4731-bb38-c0d22fbe4515:e07d0bdc-1b22-4fe1-8a05-de5689cd6dabKenneth<p>Hi,</p> <p>You can find that BLE_GATTS_VAR_ATTR_LEN_MAX is 512 bytes from:<br /><a href="https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s112.api.v7.2.0/group___b_l_e___g_a_t_t_s___a_t_t_r___l_e_n_s___m_a_x.html">https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s112.api.v7.2.0/group___b_l_e___g_a_t_t_s___a_t_t_r___l_e_n_s___m_a_x.html</a></p> <p></p> <p>However this max length include a 3 byte overhead, so the actual useable data that can be notified is ATT_MTU - 3 bytes (=509 in your case) as written here:<br /><a href="https://devzone.nordicsemi.com/support-private/support/214779#permalink=399234">https://devzone.nordicsemi.com/support-private/support/214779#permalink=399234</a></p> <p>I am little unsure why it is truncated to 507 bytes when you are using 510 or more,&nbsp;but it may be that the packet is actually split into several packets (queued writes).</p> <p>Best regards,<br />Kenneth</p><div style="clear:both;"></div>