1. Bluetooth module Serial port

The serial interface is abbreviated as a serial port, also known as a serial communication interface, generally also known as a COM port. This is a general term, and interfaces that use serial communication are called serial ports. A serial port is a hardware interface.

UART is the abbreviation for Universal Asynchronous Receiver/Transmitter, meaning Universal Asynchronous Receiver/Transmitter.

UART includes a TTL level serial port and an RS-232 level serial port, and both devices using UART communication need to comply with the UART protocol.

2. Bluetooth module UART protocol

According to the different protocol formats, it can be further divided into two protocol formats: H4 (TX/RX/CTS/RTS/GND) and H5 (TX/RX/GND)

H4:  Communication does not include re transmission, so CTS/RTS must use. UART communication is in "transparent transmission" mode, that is, the data monitored through the Logic analyzer is the actual communication data Direction Head DataType Host ->Controller 0x01 HCI Command Host ->Controller 0x02 ACL Packet Host ->Controller 0x03 SCO Packet Controller ->Host 0x04 HCI Event Controller ->Host 0x02 ACL Packet Controller ->Host 0x03 SCO Packet

H5:  (also known as 3-wire), due to support for retransmission, CTS/RTS is optional. H5 communication data packets start and end with 0xC0, that is, 0xC0... payload 0xC0. If the payload contains 0xC0, it is converted to 0xDB 0xDC; If the payload contains 0xDB, it is converted to 0xDB 0xDD

3. Bluetooth module serial port

Most Bluetooth HCI modules support H5 mode,

A small portion (such as BW101/BW104/BW151) only supports H4 mode (i.e. CTS/RTS is required)

Whether H4 or H5, during Bluetooth initialization, the protocol stack connects with the module at a baud rate of 115200bps. After the connection is successful, it jumps to a high baud rate (>=921600bps). Commonly used are 921600/1M/1.5M/2M/3M

Note: The H4 serial port configuration does not include a check bit; H5 usually uses even check. Remember to set the format when grabbing serial port data packets with Logic analyzer.

4. Case

Basic parameters

FSC-DB004-BT826 integrates BT826 Bluetooth module and DB004 pin interface board, supports Bluetooth 4.2 dual mode protocol (BR/EDR/LE), integrates baseband controller, Cortex-M3 CPU, PCB antenna

• ·Protocol: SPP, HID, GATT, etc
• ·Package size: 13 * 26.9 * 2mm
• ·Power level 1.5
• ·Default serial port baud rate: 115.2kbps Baud rate range: 1200bps~921kbps
• ·Support OTA upgrade
• ·BQB, MFI
• ·Compliant with ROHS specifications

5. Summary

Bluetooth serial communication is a very simple and basic knowledge. Generally, when debugging, read the module specification carefully, and pay attention to some matters when using the Logic analyzer. If you don't understand anything else, you can contact the Feasycom team!