3M M2256PW Determining Target Areas, Calibration Setup Stage Offset Field Size Value Description

3M™ Multi-touch Display M2256PW User Guide 23

Table 2. Calibration Setup Stage

Offset	Field		Size	Value	Description
0	bmRequestType	1		0x21	Class,H2D,Interface
1	bRequest	1		0x09	Set Report
2	wValue	2		0x0303	Msb 03 = Feature
					Lsb 03 = Feature Report ID
4	wIndex	2		0	Always 0
6	wLength	2		8	Always 8
Table 3. Data Stage
Offset	Field		Size	Value	Description
0	Report ID	1		0x03	Feature report ID
1	Report Subtype	1		0x04	Indicates a calibration request
2	bCalType	1		0x01	0x01 = Extended cal (CX)
3--7	Not used	5		0	Not used

The device stalls endpoint 0 if the command cannot be processed successfully. The request cannot be processed if an invalid calibration type is given in the wValue field. The request will also fail if the 2 calibration points do not fall within certain bounds established by the firmware. These bounds require that the 2 calibration points be in opposite quadrants of the sensor.

The host should issue a GetStatus request to determine the status of this request. The status report includes a command status byte which will be set as shown below.

Table 4. Calibration Response

Command Status Byte	Description
0	Calibration Failed
1	Controller is waiting for a touch in the lower left corner.
	Calibration software paints a target in the lower left corner.
2	Controller is waiting for a touch in the upper right corner.
	Calibration software paints a target in the upper right corner.
3	Calibration completed successfully.

The controller does not timeout waiting for touch. Use the soft reset command to abort the calibration.

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 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

3M Touch Systems, Inc. Proprietary Information – 37531 Rev D