subject: USB Connectivity With Touch Screens [print this page] The recent launch of Apple's iPad spawned a new product category: the tablet. Touch screen support has become the default human interface as tablets focus on ease of use and keyboardless design. Meanwhile, Microsoft has added touch screen support at the foundation of its Windows 7 architecture. Credit Suisse estimates more than 33 million units of large touch screen products will be sold in 2011, mainly due to these two driving forces: the growingpopularity of tablets and Windows 7 support for touch screen technology.
Most touch screen systems will connect with the host CPU or application processor through a universal serial bus (USB) interface. However, none of today's major touch screen controllers support USB natively. As a result, touch screen system integrators must "bridge" a USB microcontroller (MCU) between the host and the touch controller(s). Once an MCU is selected, developers must write the firmware code to establish the communication between the host and the MCU to support the touch screen application. Adopting a USB MCU that includes preprogrammed touch screen support can greatly simplify this firmware development task and shorten time to market.
The need for touch screen USB code is new to touch screen system integrators. They generally have no expertise in USB development as the interfaces they used in the past are usually universal asynchronous receiver/transmitter (USB to UART), serial peripheral interface (SPI) or interintegrated circuit (I2C). System integrators must develop this USB expertise internally or acquire it from third parties. In either case, software development cost increases and project delivery might be delayed. On the other hand, most companies have preferences in their MCU buying habits based on experiences such as supplier relationship, cost, supply chain and support. This further complicates the design issues as the touch screen system integrator must become familiar with various MCUs and then write different code for each.
