connection request to a known address

[Hust]

Hi guys, I want to ask if it is possible for a nrf51822 to connect to a Central ( my cell phone) without advertising. Let assume that my cell phone has nrf51822's MAC address from the first connection and it can send a connection request to nrf51822.

[RK]

No it's not. The Bluetooth protocol requires that a device be advertising before it's connectable. You can advertise yourself as connectable to only one central, but you need to advertise.

[Hust]

Thank you very much for your reply, btw, how about the power? Is advertising to only one central requires less power than undirect advertising?

[Jørgen Holmefjord]

From this blog post:

ADV_DIRECT_IND: connectable directed advertising

You use this to direct your advertise packet to one specific central to ask for connection. The packet is still a broadcast packet but other scanners will ignore the packet if the peer address is not matched with them. And connect request or scan request from unmatched central will be ignored by the advertiser. Directed advertising usually comes with high duty cycle with interval fix at 3.75ms. For low duty cycle directed advertising, it's configurable and should be <10ms. (Section 4.4.2 Part B Vol 6).

The advertising method is the same. The current consumption will depend on the advertising interval, and scan interval settings of the central. More current might be used before connection, but connection might be initiated sooner, lowering the total average current consumption.