AN249 Silicon_Laboratories, AN249 Datasheet - Page 2

• Manufacturer Part Number: AN249
• Description: Human Interface Device Tutorial
• Manufacturer: Silicon_Laboratories

AN249
2. Introduction To HID
USB devices communicate with PCs as shown in Figure 1. Creating a USB interface between an embedded
system and a PC requires writing code for the following software subsystems:
2.1. USB System Development
USB specification defines a number of USB classes, such as HID, mass storage devices, etc. Developers creating
a USB system that does not fit into one of the pre-defined USB classes must develop custom drivers along with
device firmware and PC applications. For these systems, developers can use a software package such as Silicon
Laboratories USBXpress, which includes a set of custom drivers, firmware routines, and host routines that enable
USB communication. HID-class devices simplify USB communication one step further by using a standardized,
flexible driver that comes pre-installed with all commonly used operating systems.
Benefits of developing with HID include:
2.2. Getting Started With HID
Designers can create embedded HID firmware using the Silicon Laboratories IDE, the evaluation version of the
Keil compiler, and the target board included in the Silicon Laboratories development kit. Designers developing
host-side PC applications must install the Windows Driver Development Kit (DDK), which can be downloaded from
http://www.microsoft.com/whdc/devtools/ddk/. Once the DDK is installed, the developer will be able to take
advantage of HID-specific API calls to send and receive data with HID-based devices.
For designers creating an HID-based system using this application note's associated firmware template as a
starting point, the typical system design flow is shown in Figure 2.
2
Embedded device firmware
Host-side operating system drivers
Host-side PC application
Compatibility with all commonly used operating systems (XP, 2000, Mac, Linux)
No need for driver development or distribution
Streamlined device/host interface due to standardized but flexible HID specifications
Device Firmware
USB Device
Figure 1. USB Interface between a PC and an Embedded System
Bi-directional Data Flow
Rev. 0.2
System Drivers
System-
Buffers
Level
Data
PC
Application
Host-Side