AR1000_16 Datasheet, PDF (39/61 Pages) Microchip Technology – AR1000 Series Resistive Touch Screen Controller

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.
1. Disable touch reporting by issuing <Disable
Touch> command.
Send: <0x55><0x01><0x13>
Receive: <0x55><0x02><Response><0x13>
2. 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>
3. Calculate the CalibrationInset register’s address
by adding its offset value of 0x0E to the register
group Start address of 0x20.
Register Address = Register Start Address +
CalibratioInset Register Offset = 0x20 + 0x0E = 0x2E
4. 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
5. 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>
6. Issue the CALIBRATE_MODE command.
Send: <0x55><0x02><0x14><0x04>
Receive: <0x55><0x02><0x00><0x14>
7. 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
Touch and
Release Target
8. 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>
9. 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
Touch and
Release Target
10. Wait for the user to touch and release the
second calibration point target. Do this by
looking for a controller response of:
<0x55><0x02><0x00><0x14>
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DS40001393C-page 39