Touch screen system integrators with a simple and easy‐to‐use USB bridge solution

Touch screen system integrators with a simple and easytouse USB bridge solution

The CP2501 features a twowire, bidirectional serial system management bus (SMBus) that complies with the System Management Bus Specification, version 1.1, and is compatible with the I2C serial bus. Reads and writes to the interface are byte oriented, with the SMBus interface autonomously controlling the serial data transfer. Clocklow duration can be extended to accommodate devices with different speed capabilities on the same bus. The SMBus interface consists of the SMBus_SCL (serial clock) and SMBus_SDA (serial data out) signals and is programmable to support a wide range of clock speeds.

The system firmware checks the user firmware space for the key signature. If the signature is present, USB enumeration is handled by the user firmware using the interface API. When the user firmware initializes the USB interface using the interface API, the system firmware uses the usercustomized descriptors generated by the CP250x configuration wizard to enumerate as a USB mouse or a touchscreen device. If the key signature is not present, the system firmware assumes that the user firmware has not been programmed and uses the default bootloader descriptors to enumerate. With the default bootloader descriptors, the CP2501 device appears as a standard HID class device that supports only the features required for bootloading. After enumeration, the host begins generating the interrupt transfer requests, and the device prepares the data to be transferred. All initialization firmware and the USB interface firmware including the configurable descriptors are generated by the configuration wizard. The developer only needs to add proprietary algorithms and bridge the data using the API provided. Having an effective USB microcontroller within the CP2501 device is only half the job. To ease development, the CP2501 is backed by a configuration wizard that enables the developer configure a USB communication system quickly and easily. The configuration wizard features several tabs, each for a different function such as device, communication, touch, pen, mouse and GPIO. This flexible, easytouse development tool enables developers to create the firmware project files, customize USB parameters, set the touch screen resolution and generate USB HID touch screen descriptors.

The configuration wizard output represents a complete project that allows the developer to add the code needed to communicate with the touch screen. All initializations for the chosen serial interface as well as the USB descriptor generation and initialization are complete. The developer simply makes calls to the system firmware API to bridge data. Having all of the lowlevel USB functionality complete and working drastically reduces the time and effort of USB development. Without any additional modifications, the project generated by the configuration wizard will enumerate properly on a Windows machine. The device appears in the device manager as an HIDdevice. In Windows Vista and Windows 7, the computer properties will show that a singletouch or multitouch device is connected.

Summary

The CP2501 controller provides touch screen system integrators with a simple and easytouse USB bridge solution. This highly integrated, HID Classcompliant solution reduces development time and cost and eases the frustration of implementing a USB interface from scratch. The addition of the developeraccessible MCU core, onchip memory and other resources enables the touch screen developer to offload performanceenhancing or operating system compliance algorithms from the touch controllers and/or the host system itself. Ultimately, the CP2501 controller helps liberate touch screen system integrators from mundane but necessary communication software development, enabling them to focus their time and resources on what they do best: developing intuitive, userfriendly touch screen interfaces.

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