SC500 USB Controller Communications
21
3M Touch Systems Proprietary Information
Set Feature – Calibration
This is a request to perform a 2-point calibration. The calibration can be performed at
points inset from the lower left, upper left and upper right corners. The 2-point
calibration defines the active area of the touch screen by mapping two targets
displayed on the video image to absolute X and Y coordinates on the touch screen.
Table 11. Set Feature- Calibration
Offset
Field
Size Value
Description
0
bmRequestType 1
0x21
Host to device
1 bRequest
1
0x09
Set
Report
2 wValue 2
0x0303
03=Feature
03=Feature ID
4 wIndex 2
0 Always
0
6 wLength
2
8 Always
8
Table 12. Data Stage
Offset
Field
Size Value
Description
0
Report ID
1
0x21
Host to device
1
Report subtype
1
0x04
Set Report
2
bCalType
1
0xXX
0x01 = Extended Calibration (CX)
0x02 = Corner Calibration (CN)
3
Not used
5
0
Not used
Response
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.
During the calibration process, the calibration software polls the Get Status command
to monitor the progress of the calibration.
The calibration will fail if the two calibration points do not fall within certain bounds
established by the firmware. These bounds require that the two calibration points be in
correct quadrants of the sensor.
Calibration software can abort the calibration process with a Reset Request.
During the calibration process, the controller automatically determines screen/display
orientation and touch screen connector pinouts. This information is saved in the
controller non-volatile memory.
