2016 Microchip Technology Inc. DS50002466A-page 59
RN4870/71 BLUETOOTH
®
LOW ENERGY MODULE
USER’S GUIDE
Appendix A. Bluetooth Low Energy Fundamentals
A.1 INTRODUCTION
When two BTLE devices must be connected, one device must be in Central role and
the other in Peripheral role. The Peripheral device advertises to show its connectable
status, while the Central device scans service advertisements, and if required, initiates
a connection to the Peripheral device. Once connected, either end of the connection
can choose to bond. Once bonded, all security related keys are saved and security pro-
cess are waived when reconnecting. Bonded peripheral device can only perform direct
advertise, therefore, no longer is able to connect to device other than its bonded peer.
Similar to Bluetooth Classic, BTLE uses the concept of profiles to ensure
interoperability between different devices. As illustrated in Figure A-1, BTLE profiles
are collection of services. All BTLE services are built on top of the Generic Attribute
Profile (GATT), where GATT defines accessibility of attributes called characteristics.
Therefore, the main functionality of the BTLE profiles is built around the characteristics.
Those devices that maintain the value of characteristics in a service are called the
Server of the Service. On the other hand, those devices that acquire data from their
peer are called Client.
Each service and its characteristics can be identified by its UUID. The UUID takes
either a16-bit short form or a 128-bit long form. As specified in the Bluetooth Core Spec-
ifications, all Bluetooth SIG adopted public services and characteristics have short
UUIDs, while the user defined private UUIDs are in long form. For the details of Blue-
tooth SIG adopted services and characteristics, please refer to
https://developer.bluetooth.org/gatt/profiles/Pages/ProfilesHome.aspx.
The accessibility of each characteristic is defined by a 8-bit characteristic property in
bitmap format, as shown in Ta ble A - 1.
TABLE A-1: CHARACTERISTIC PROPERTIES
Property Bitmap Description
Extended Property
(1)
0b10000000 Additional property available
Authenticated Write
(1)
0b01000000 Write characteristic with authentication from client to
server
Indicate 0b00100000 Indicate value of characteristic with acknowledgment
from server to client
Notify 0b00010000 Notify value of characteristic without acknowledgment
from server to client
Write 0b00001000 Write value of characteristic with acknowledgment
from client to server
Write without
response
0b00000100 Write value of characteristic without acknowledgment
from client to server
Read 0b00000010 Read value of characteristic. Value is sent from server
to client
Broadcast
(1)
0b00000001 Broadcast value of characteristic
Note 1: Currently not supported in RN4870
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