SWRA751 September 2022

1 Introduction

Bluetooth® systems consists of a host and a controller. The BT SIG has created a standard protocol for the host to communicate with the controller. This is called the Host Controller Interface (HCI) which is specified in the BT Core 4.1 specification Volume 2 Part E. The HCI provides a uniform command interface to a Controller. There are some commands which are not listed in the specifications and they are specific to the device itself. These commands are vendor-specific commands (VS) generally used for testing and debugging purposes. For further details on testing command sequences, refer to CC256x Testing Guide.

Figure 1-1 HCI Commands VS

As shown in the diagram above, the host (MSP430) sends HCI commands to the controller (CC256x). The controller then sends HCI events to the host as a response to the HCI commands. All HCI commands follows this format for all packets:

Table 1-1 HCI Packet Format

First Byte	Next Bytes
HCI Packet Type	HCI packet (variable length)

All HCI commands starts with a byte describing type of packet while the remaining bytes is dependent on the type of HCI packet.

Here is a list of important HCI packet types:

Table 1-2 HCI Packet Types

HCI Packet Type	Packet Type Indicator	Direction
HCI command packet	0x01	Host to baseband controller
HCI event packet	0x04	Baseband controller to host