Apple Tech Reviews

Using Usb Connectivity To Integrate Contact Screens In Computing Purposes

Introduction

The current launch of Apple’s iPad spawned a brand new product class: the tablet. Contact display screen support has change into the default human interface as tablets deal with ease of use and keyboardless design. In the meantime, Microsoft has added contact screen support on the basis of its Home windows® 7 architecture. Credit Suisse estimates more than 33 million models of huge contact display products will likely be bought in 2011, mainly on account of these {two} driving forces: the growing recognition of tablets and Windows 7 help for touch screen technology.

Most touch display screen systems will join with the host CPU or utility processor by a universal serial bus (USB) interface. However, none of in the present day’s main contact display controllers help USB natively. In consequence, touch screen system integrators should “bridge” a USB microcontroller (MCU) between the host and the contact controller(s). Once an MCU is chosen, builders should write the firmware code to establish the communication between the host and the MCU to help the contact display screen application. Adopting a USB MCU that features preprogrammed
touch screen support can enormously simplify this firmware improvement task and shorten time to market.

Fortuitously, touch display screen system integrators have one more various to growing USB expertise or buying thirdget together USB software: combine a preparedmade USB bridge silicon/software program resolution that requires no USB expertise on the part of the developer.

Human Interface Machine (HID) Overview

In line with the USB Implementers Forum, the USB communications structure is designed to allow computing devices akin to desktop PCs and laptops to interconnect with many different peripheral devices. A USB uses a {two}wire serial communications hyperlink operating at certainly one of three
totally different speeds: 1.5 megabits per second (lowpace), 12 Mbps (fullspeed) and 480 Mbps (excessivespeed). USB units are categorized into numerous system courses corresponding to show, communication, audio, mass storage and human interface.

The Human Interface Machine (HID) Class defines widespread behaviors and features for touch display screen interfaces. The HID class contains peripherals equivalent to keyboards, mice, trackballs, joysticks, touch pads and contact screens that allow end customers to manage and interact with the computing system. HID also contains provisions for output directed to the top user.
The management pipe typically handles enumeration and machine configuration whereas the interrupt pipe is used for information transfer. Descriptors define a USB device to the host regarding the type of device, the system producer, USB1.x or 2.0 or 3.zero support, gadget configuration,
endpoints quantities and kinds, etc.

A HID report is used to transmit HID management data to and from an HID Class device. A report descriptor defines the report format. Input and output experiences specify control knowledge and feature studies specifying configuration data. When a couple of report of the same kind is required for a particular gadget, every report receives a unique report ID. Enter and output reports specify HID control data. Input controls include information related to an utility such as the coordinates of a finger. Output controls are a sink for application data similar to lighting up a show or activating a touch sensor. A feature report specifies configuration information for a specific device. A consumermode software can get hold of feature information by utilizing this report designation.

The HID enumeration requires the system to send an HID descriptor, which accommodates details about all of the knowledge and its formats. Report descriptors sent to the host determine the report format. All experiences are preceded by a report ID, which describes how the host and the device
determine the actual report and the way data is parsed between a number of reports. Each bit within the report is specified by report size and report depend identifiers. For instance, a report measurement of one and a report depend of {two} identify {two} bits. This instance could be the definition of a set of
finger touches. To ship a whole byte, the report measurement would be set to eight bits. Formatting the information into reports helps to prepare the information by way of information widths in order that the host and finish units know find out how to parse the data.

USB Contact Display screen Bridge Resolution
The CP2501 system is a contact display USB bridge that can be utilized to connect the touch display controller with the host CPU. The CP2501 incorporates a highefficiency MCU with a 48 MIPS 8051suitable core, fifty three kB of consumerprogrammable flash memory and 3.5 kB of RAM. In contrast to
other USB MCU units in the market, the CP2501 features preprogrammed USB touch interface firmware, which drastically simplifies USB touch display product development. The Home windows 7 touch interface compliant CP2501 system works seamlessly with the Windows digitizer class driver for touch screens and is supported by Silicon Labs’ GUIprimarily based configuration wizard. This deployment instrument allows developers to easily and quickly connect their touch controller to a USB system with out having to develop customized USB firmware, thus lowering time to market as well as the level of expertise required for USB interface development.

The CP2501 machine features a USB 2.zerocompliant, fullspeed USB controller with an integrated fullspeed transceiver and onchip matching and pullup resistors. The built-in USB controller manages all data transfers on the USB bus, as well as command requests generated by the USB host controller. The person firmware makes use of the interface offered by the system firmware to initialize and talk utilizing the USB protocol. The CP2501 device additionally features a USB bootloader to easily replace user firmware. Consumer code is required to enable the interface API to
initialize the USB interface and send touch knowledge to the host PC.

The CP2501 system supports three completely different serial interfaces for communicating with numerous contact display controllers. The interface alternative will be chosen by way of the CP250x configuration wizard. The CP2501 machine’s UART interface consists of the UART_TX (transmit) and UART_RX (receive) knowledge indicators and is programmable to support a wide range of knowledge formats and baud rates. The SPI protocol provides access to a versatile, fullduplex synchronous serial bus. SPI operates as a grasp gadget in fourwire mode.

The CP2501 includes a {two}wire, bidirectional serial system administration bus (SMBus) that complies with the System Administration Bus Specification, version 1.1, and is appropriate with the I2C serial bus. Reads and writes to the interface are byte oriented, with the SMBus interface autonomously controlling the serial knowledge transfer. Clocklow period might be prolonged to accommodate units with totally different speed capabilities on the identical bus. The SMBus interface consists of the SMBus_SCL (serial clock) and SMBus_SDA (serial data out) signals and is
programmable to assist a variety of clock speeds.

The configuration wizard output represents a whole undertaking that enables the developer so as to add the code needed to speak with the touch screen. All initializations for the chosen serial interface as well as the USB descriptor generation and initialization are complete. The
developer merely makes calls to the system firmware API to bridge data. Having all the low level USB performance full and dealing drastically reduces the effort and time of USB development. Without any extra modifications, the challenge generated by the configuration
wizard will enumerate properly on a Home windows machine. The device seems within the gadget manager as an HIDdevice. In Windows Vista and Home windows 7, the pc properties will present {that a} singlecontact or multicontact device is connected.

Summary
The CP2501 controller supplies touch display screen system integrators with a easy and simpletouse USB bridge solution. This extremely integrated, HID Classcompliant answer reduces improvement time and value and eases the frustration of implementing a USB interface from scratch. The
addition of the developeraccessible MCU core, onchip memory and different sources allows the touch display screen developer to offload performanceenhancing or working system compliance algorithms from the touch controllers and/or the host system itself. Finally, the CP2501
controller helps liberate touch display system integrators from mundane but essential communication software program improvement, enabling them to focus their time and sources on what they do finest: developing intuitive, personpleasant contact screen interfaces.

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