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BU21023GUL Datasheet(PDF) 10 Page - Rohm |
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BU21023GUL Datasheet(HTML) 10 Page - Rohm |
10 / 21 page BU21023GUL BU21023MUV BU21024FV-M 10/17 TSZ02201-0L5L0F300840-1-2 © 2013 ROHM Co., Ltd. All rights reserved. 7.June.2016 Rev.004 www.rohm.com TSZ22111・15・001 Background Information A resistive touch screen is made up of multiple layers of sandwiched resistive films and protective coatings all sitting on top of an LCD display. Resistive touch screens work by direct contact of a stylus or a finger flexing a pair of resistive films, hence any blunt pointing instrument or a gloved finger may be used. Touch screen resolution The resolution of a touch screen is typically measured in dots per inch (dpi) and is a function of the physical size of the touch screen and the ADC used in the conversion circuitry. For example, a 3.5 inch x 5 inch screen used with the BU21023 devices can provide a theoretical resolution of 1024 /5 = 204 dpi. In the case of resistive touch screens, the direct contact nature of its operation and finger thickness often impose an upper limit on the effective system resolution that may be achieved, regardless of the resolution of the ADC itself. Description of Function The BU21023 devices connect to a standard 4-wire resistive touch screen on one side and to a HOST processor on the other side. The BU21023 include the analog and digital circuitry to process and provide dual touch coordinate data and pinch, spread gesture information to the HOST . The BU21023 devices include an internal CPU and provide a high degree of programmability by exposing a set of registers that can be accessed by a HOST through SPI or 2-wire serial interfaces. The IFSEL pin determines whether SPI or 2-wire serial interface is selected, The BU21023 devices include an INT pin whose polarity can be programmed via registers. When an interrupt occurs, for example, due to touch detection, the HOST processor is required to read an interrupt status register to determine the cause of the interrupt and take appropriate action. The program memory of the internal CPU may be initialized via the HOST interface or via an external EEPROM. This is selected by a register setting. The BU21023 devices support two sensing modes; continuous and interval sensing modes, that are register- selectable. In the continuous sensing mode, the embedded CPU reads Z, X & Y coordinates continuously when a touch is detected. The interval sensing mode allows a delay to be inserted between each cycle. The BU21023 devices enable optimization of touch detection threshold for a given screen. They also include several sophisticated calibration algorithms. Often, a description of the registers followed by flow charts requires application note to explain the steps in finer detail. The application note also includes information on touch screen parameters that one should look for when selecting resistive touch screens for multi-touch. |
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