Guidelines For The C3 Commands - 3M Touch Screen Controller RX142 Reference Manual

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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.
3M™ MicroTouch™ Controller RX142 Reference Guide
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