BU21023GUL

BU21023MUV

BU21024FV-M

9/16

Datasheet

Datasheet

TSZ02201-0L5L0F300190-1-2

© 2014 ROHM Co., Ltd. All rights reserved.

31.Mar.2014 Rev.003

www.rohm.com

TSZ22111・15・001

BU21024FV-M

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”x5” screen used with the BU21024 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 BU21024 devices connect to a standard 4-wire resistive touch screen on one side and to a HOST processor on the

other side. The BU21024 includes four additional sense terminals allowing it to be used with either 4-wire or 8-wire resistive

touch screens. The BU21024 include the analog and digital circuitry to process and provide dual touch coordinate data and

pinch, spread gesture information to the HOST .

The BU21024 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 I

is selected, The BU21024 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 BU21024 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 BU21024 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 other document to explain the steps in finer detail.

The other document also includes information on touch screen parameters that one should look for when selecting resistive

touch screens for multi-touch.