BLE-USB, USB to Bluetooth Low Energy Converter (Ver. 1.0, Oct/6/2016) 9
The Broadcaster and Observer has used in the broadcast mode.
1.5.1 Master and Slave
First, there is the concept of Master (Central)/ Slave (Peripheral), which has to do with
establishing a link. This is also known as the GAP role. A Peripheral can advertise, to let other
devices know that it's there, but it's only a Central that can send a connection request to
establish a connection. When a link has been established, the Central is also called a Master,
while the Peripheral could be called a Slave. The Slave only can connect to a Master, but the
Master can connect to three Slaves in our module. The Slave will not be sending broadcast
packet after link has been established.
Figure 1-5. The workflow of Bluetooth LE connection
The Slave has two broadcast patterns. One is the high discoverable mode. The other is low
discoverable mode. The Slave will be broadcasting for 30 second in high discoverable mode,
and the broadcast interval is 20ms for 3 channels. The Slave will be broadcasting for 60 second
in low discoverable mode, and the broadcast interval is 640ms for 3 channels. The Slave will in
the high discoverable mode after power on. If the Slave didn’t received connection request from
the Master in high discoverable mode and it will switch to low discoverable mode.
1.5.2 Broadcaster and Observer
The Broadcaster does so by constantly advertising, and the Broadcaster usually has useful data
in the advertising packet. The advertising packet is meant for everyone to see. The Broadcaster
is broadcasting to others, so it never accepts connections. The Observer is the opposite of the
Master
(Central)
Slave
(Peripheral)
Slave
(Peripheral)
Scan
Broadcast packet
Connection Request
Link establish
Broadcast packet
Scan
Broadcast packet
Connection Request
Link establish
