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34 3M™ Multi-touch Display M2256PW User Guide
3M Touch Systems, Inc. Proprietary Information – 37531 Rev D
Calibrate Procedure
To use the CX command:
1. Enter the Calibrate (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.
3. Touch the sensor at an upper right 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, you
must start over again.
Touching the two valid calibration points results in a successful calibration. If either
calibration point is invalid, the calibration fails. The PX controller restores the previous
calibration values. If Calibrate fails, repeat the CX process.
Guidelines for Calibrate Command
Here are several guidelines for using the Calibrate 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 (NOVRAM). Therefore, you
do not have to calibrate the sensor each time you power on the system. You should,
however, recalibrate the touch sensor any time the video display changes size or
resolution.
• You can cancel calibration at any time during this sequence by issuing a Reset
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, the resolution of your Windows-based display is 1680
x 1050. The Calibrate Extended command calculates the amount to move inward as
follows:
•
Amount to move inward in the X direction: 1680 x 1/8 = 210
•
Amount to move inward in the Y direction: 1050 x 1/8 = 131
The Calibrate Extended command then positions the first calibration target inward from
the lower left corner (0,1049) and the second calibration target inward from the upper
right corner (1679,0). The following illustration shows how the calibration targets are
calculated for a Windows-based system. Your operating system may be different.