The Basic Knowledge of Bluetooth Module

- Oct 26, 2018-

1. Data transmission

The Bluetooth module can transmit data through the serial port (SPI, IIC) and MCU control device.

The Bluetooth module can be used as a master and a slave. The host is able to search for other Bluetooth modules and actively establish a connection; the slave cannot actively establish a connection, only wait for others to connect themselves.

2. Low power consumption

Bluetooth Low Energy, referred to as BLE. Bluetooth low energy wireless technology uses many intelligent means to minimize power consumption.

The Bluetooth low energy architecture consists of two chips: a single-mode chip and a dual-mode chip. The Bluetooth single-mode device is a new chip in the Bluetooth specification that only supports Bluetooth low energy technology - part of a technology optimized for ULP operation. The Bluetooth single-mode chip can communicate with other single-mode chips and dual-mode chips. In this case, the latter needs to use the Bluetooth low energy technology part of its own architecture to send and receive data. Dual-mode chips can also communicate with standard Bluetooth technology and other dual-mode chips using traditional Bluetooth architecture.

3. Bluetooth protocol

The protocols in the Bluetooth protocol system are divided into four layers according to the level of attention of the SIG:

(1) Core protocols: BaseBand, LMP, L2CAP, SDP;

(2) Cable replacement agreement: RFCOMM;

(3) Telephone transmission control protocol: TCS-Binary, AT command set;

(4) Selection protocol: PPP, UDP/TCP/IP, OBEX, WAP, vCard, vCal, IrMC, WAE.

4. The underlying hardware module

(1) Radio frequency module (Radio): The bottom layer of Bluetooth, with a microstrip antenna, responsible for data reception and transmission.

(2) Baseband module (BaseBand): Wireless medium access convention. Provides synchronous connection-oriented physical links (SCO) and asynchronous connectionless physical links (ACLs), which are responsible for frequency hopping and Bluetooth data and information frame transmission, and provide different levels of error correction (FEC and CTC).

(3) Link Control Module (LC): Encoding and decoding of Bluetooth packets.

(4) Link Management Module (LM): responsible for creating, modifying, and publishing logical links, updating physical link parameters between devices, and performing link security and control.

(5) Host Controller Interface (HCI): is a software and hardware interface part, consisting of a baseband controller, connection manager, control and event registers; the software interface provides a unified command of the underlying hardware to explain the upper and lower layers of messages and data transfer. The hardware interface includes UART, SPI, USB, and so on.

5. Intermediate protocol layer

(1) Logical Link Control and Adaptation Protocol (L2CAP): The basis of the Bluetooth protocol stack and the basis for other protocol implementations. Provides connection-oriented and connection-free data encapsulation services to the upper layer; adopts multi-channel technology, segmentation and recombination technology, group extraction technology for protocol multiplexing, segmentation and reassembly, authentication service quality, group management and other behaviors.

(2) Audio and Video Distribution Transmission Protocol (AVDTP) and Audio Video Control Transmission Protocol (AVCTP): Both are mainly used for the transmission of Audio/Video in Bluetooth devices, the former is used to describe transmission, and the latter is used to control signal exchange format and mechanism.

(3) Service Discovery Protocol (SDP): The Bluetooth technology framework is a critical layer, based on all application models. Dynamically query device information and service types, establish a corresponding service communication channel, and provide the upper layer with service types and attribute protocol information that are found to be available.

(4) Serial Port Simulation Protocol (RFCOMM): The 9-pin RS232 serial port function is simulated to realize serial communication between devices.

(5) Binary Telephone Control Protocol (TCS): A bit-oriented protocol based on ITU-T Recommendation Q.931, which defines Call Control Signalling for establishing voice and data calls between Bluetooth devices and is responsible for handling the mobile management process of the Bluetooth device group.

6. Bluetooth Profile

The Bluetooth Profile is a wireless interface specification for data communication between Bluetooth devices. There are currently four major categories and thirteen protocol rules, and vendors can customize specifications. Several of the most common profile files:

(1) Generic Access Profile (GAP): The basis for all other profiles, defines a common method for establishing a baseband link between Bluetooth devices, and allows developers to define new profiles based on GAP. Contains all the functions implemented by Bluetooth devices, common steps for discovering and connecting devices, basic operations such as basic user interfaces.

(2) Service Discovery Application Profile (SDAP): Describes how the application discovers remote device services using SDP, and can connect to SDPs that send/receive service queries to/from other Bluetooth devices.

(3) Serial Port Profile (SPP): Defines how to set up a virtual serial port and how to connect two Bluetooth devices based on the ETSI TS 07.10 specification. The speed can reach 128kb/s.

(4) Generic Object Exchange Profile (GOEP): Any object (such as pictures, documents, etc.) can be transferred from one device to another.



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