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3M™ MicroTouch™ Controller RX142 Reference Guide

3M Touch Systems, Inc. Proprietary Information

In addition to scaling the Format Tablet output to the display, this command corrects for

sensor orientation and sensor pinout variations. This information will be maintained by

the controller. The Calibrate 3 Point command initiates an interactive calibration

procedure which defines the active area of the sensor by mapping locations to an absolute

X,Y coordinate system. Touch points generated subsequent to a successful calibration

operation are calculated based upon these calibration points. Calibrate 3 Point utilizes

inset calibration points located 12½ percent inboard from the sensor corners (at touch

X,Y locations 128,128, 895,895 and 128,895) for accuracy and ease of operation.

Guidelines for the C3 Commands

Here are several guidelines for using the C3 commands:

• The controller uses the data immediately before liftoff to register a calibration touch.

Therefore, you can touch the coordinate target, hold for a few seconds, and then lift

off. Instructing users to touch this way results in a more accurate calibration.

• The controller stores the data in non-volatile memory. Therefore, you do not have to

calibrate the sensor each time you power on the system. You should, however,

recalibrate the sensor any time the video display area changes physical size.

• You can restart calibration at any time during this sequence by issuing a Reset

command and reissuing a C3 command.

Determining Target Areas

The default calibration targets (points) are located 12.5% (1/8) inward from the corners of

the video image. For example, suppose the display resolution of your monitor is 1024 x

768. The C3 calculates the amount to move inward as follows:

• Amount to move inward in the X direction: 1024 x 1/8 = 128

• Amount to move inward in the Y direction: 768 x 1/8 = 96

The C3 command then positions the first calibration target inward from the lower left

corner and the second calibration target inward from the upper right corner. Figure 2

shows how the calibration targets are calculated.