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•
The controller uses the data immediately before liftoff to register a calibration touch.
Therefore, you can touch the sensor, move your finger to the 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 (NOVRAM). 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 changes size or resolution.
•
You can restart calibration at any time during this sequence by issuing a Reset
command and reissuing a CX 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 display is 1024 x
768. The Calibrate Extended command 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
•
Lower Left Calibration Target
X = 0 + (1024 x 1/8) = 0 + 128 = 128
Y = 767 - (768 x 1/8) = 767 - 96 = 671
*The coordinates are in video terms, with the origin (0, 0) in the upper left corner of the sensor. Examples from the
controller's perspective, however, place the origin at the lower left corner of the sensor (numbers in brackets). The
controller outputs 0 to 64K on both axes independent of display screen resolution.
The Calibrate Extended command then positions the first calibration target inward from
the lower left corner and the second calibration target inward from the upper right corner.
The following illustration shows how the calibration targets are calculated.
Calibrate Extended Procedure
To use the CX command:
1. Enter the Calibrate Extended (CX) command. The controller sends an initial
acknowledgment of <SOH>0<CR>.
2. Touch the sensor at a lower left target, which is located 12.5% (1/8) in from the
corner of the video image. The controller returns an acknowledgment of
<SOH>1<CR>. This is a positive response. If you receive a negative response
<SOH>0<CR>, you can cancel the calibration by issuing a Reset command and then
start over again.
(0, 0) [0, 0]*
(128, 671)
(0, 767) [0, 1024]*
3M Touch Systems, Inc. Proprietary Information – TSD-40848A
3M™ MicroTouch™ Controller EX Dual Mode Reference Guide
(
1023, 0) [1024, 0]*
(895, 96)
Upper Right Calibration Target
X = 1023 – (1024 x 1/8) = 1023 – 128 = 895
Y = 0 + (768 x 1/8) = 0 + 96 = 96
[1024, 1024]*
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