AR1011-ISLASHML datasheet(39/61 Pages) MICROCHIP

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 2009-2016 Microchip Technology Inc.

DS40001393C-page 39

AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER

10.0

APPLICATION NOTES

10.1

Calibration of Touch Sensor with

Controller

The reported coordinates from a touch screen

controller are typically calibrated to the application’s

video display. The task is often left up to the host to

perform. This controller provides a feature for it to send

coordinates that have already been calibrated, rather

than the host needing to perform this task. If enabled,

the feature will apply pre-collected 4-point calibration

data to the reported touch coordinates. Calibration only

accounts for X and Y directional scaling. It does not

correct for angular errors due to rotation of the touch

sensor on the video display.

The calibration process can be canceled at anytime by

sending a command to the controller.

Upon completion of the calibration process, the

calibration data is automatically stored to the EEPROM

and “Calibrated Coordinates” is enabled.

The process of “calibration” with the controller is

described below.

Disable touch reporting by issuing <Disable

Touch>

command.

Send:

<0x55><0x01><0x13>

Receive: <0x55><0x02><Response><0x13>

Get register group Start address by issuing

REGISTER_START_ADDRESS_REQUEST

command.

A register Start address of 0x20 is used below, for

this example.

Send:

<0x55><0x01><0x22>

Receive: <0x55><0x03><0x00><0x22><0x20>

Calculate the CalibrationInset register’s address

by adding its offset value of 0x0E to the register

group Start address of 0x20.

CalibratioInset Register Offset = 0x20 + 0x0E = 0x2E

Calculate

the

desired

value

for

the

CalibrationInset register.

A Calibration Inset of 12.5% is used below for this

example.

CalibrationInset = 2 * Desire Calibration Inset % = 2 *

12.5 = 25 = 0x19

Set the Calibration Inset by writing the desired

value to the CalibrationInset register.

Send:<0x55><0x05><0x21><0x00><0x2E><0x01

><0x19>

Receive: <0x55><0x02><0x00><0x21>

Issue the CALIBRATE_MODE command.

Send:

<0x55><0x02><0x14><0x04>

Receive: <0x55><0x02><0x00><0x14>

Software must display the first calibration point

target in the upper left quadrant of the display

and prompt the user to touch and release the

target.

FIGURE 10-1:

SUGGESTED TEXT FOR

FIRST CALIBRATION

TARGET

Wait for the user to touch and release the first

calibration point target. Do this by looking for a

controller response of:

<0x55><0x02><0x00> <0x14>

Software must display the second calibration

point target in the upper right quadrant of the

display and prompt the user to touch and

release the target.

FIGURE 10-2:

SUGGESTED TEXT FOR

SECOND CALIBRATION

TARGET

10. Wait for the user to touch and release the

second calibration point target. Do this by

looking

for

controller

response

of:

<0x55><0x02><0x00><0x14>

Touch and

Release Target

Touch and

Release Target

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