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16
Communication Basics
This section provides information on sending firmware commands to the controller
and interpreting the responses that the controller returns. The default operation of the
SC500 USB controller is USB Rev 1.1.
The USB command set is implemented by using vendor requests and vendor reports,
i.e., vendor specific transactions. The controller issues some reports without
prompting the computer. The computer can also send requests to the controller to
change how it operates or receives information about the controller. The controller
issues a synchronous report in response to some of these requests.
You need to know product ID (0102H) and the vendor ID (0596H) to write your own
driver. These values are required for identifying the controller.
The SC500 USB command set utilizes the HID protocol. The HID protocol allows the
controller to be used on most computers with operating systems that supports HID.
The only required software is a calibration tool used for aligning the touch screen to
the display. This calibration tool is available from 3M Touch Systems.
Receiving Reports from the Controller
The controller sends a variety of reports to the computer. The first byte of each report
is the Report ID that defines the structure and content of the report. The controller
sends some reports as a direct response to a computer request (synchronous). The
controller will also send some reports as the result of an external event, such as a
touch (asynchronous).
HID and Packed Touch Reports
The controller sends to the computer reports in response to touches on the touch
screen. The controller normally uses the HID-compatible report. In addition to the
HID-compatible report, there are two versions of packed report available. These
versions return up to two points of data per touch, as opposed to the one touch point in
the HID-compatible report.
The first byte of each report contains the Report ID as shown in Table 3. You can use
the Set Asynchronous Report request to toggle between report types.
Table 3. Asynchronous Reports
Name
REPORT_ID_HID
REPORT_ID_PACKED
REPORT_ID_UTILITY
Only custom drivers and software can make use of the packed coordinate format.
Refer to the Set Asychronous Report section for details on using packed coordinate
data.
Report ID
1
2
7
3M Touch Systems Proprietary Information
SC500 USB Controller Reference Guide
Description
HID-compatible coordinate data
Packed coordinate data for custom
driver
Packed coordinate data for utilities
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