# Introduction

The purpose of this document is to describe the Texas Instruments Inc. (TI) vendor specific Host Controller Interface (HCI) for Bluetooth® low energy (BLE).

## Functional Overview

In BLE, there is a logical distinction between the Host software (often referred to as the higher layer stack) and the Controller software as shown below.

BLE Protocol Stack Layers

These components can either exist on the same device (single-device configuration), or be placed on separate devices (dual-device configuration) utilizing a Host Controller Interface (HCI) for communication. In the single-device configuration, there is obviously only one device, and the application software would execute on top of the BLE profiles and stack.

Single Device Configuration

In the dual-device configuration, the application software would also execute on top of the BLE profiles and stack, and only the controller would be located on a separate device.

Dual Device Configuration

## Numerical Notation Conventions

Multiple-octets may be specified in hexadecimal notation in one of two ways:

### Standard Hexadecimal Notation

In this notation, a single hexadecimal radix indicator “0x” precedes the entire value. The octet order as read from left to right is from most significant octet to least significant octet. For example, for the value 0x123456ABCDEF, ’12’ is the most significant octet and ‘EF’ is the least significant octet.

### Colon Separated Hexadecimal Notation

In this notation, the hexadecimal radix indicator “0x” is not used and octets are colon separated. The octet order as read from left to right is from least significant octet to most significant octet. For example, for the value 12:34:56:AB:CD:EF, ’12’ is the least significant octet and ‘EF’ is the most significant octet.