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30 3M™ Multi-touch Display M2256PW User Guide
3M Touch Systems, Inc. Proprietary Information – 37531 Rev D
Controller Default Settings
Communication Parameters
The operation of the PX serial controllers is N81 (no parity, 8 data bits, and 1 stop bits)
at 115,200 baud (nonadjustable).
Data Format
Data format refers to the type of packet the controller uses to send the X/Y touch
coordinates to the host system. Format Tablet Multitouch is the default format for the
3M™ PX serial controller. In Format Tablet Multitouch, the controller sends 6 bytes per
point and provides the most rapid response time to a touch.
Refer to the Format Tablet Multitouch command in the firmware reference section. Note
that 3M MicroTouch Software automatically sets communications parameters to N81.
Operating Mode
The operating mode specifies the conditions under which the controller sends the X/Y
touch coordinates (input data packet) to the host system.
Mode Stream is the default operating mode for the PX serial controller. In Mode Stream,
the controller sends a continuous stream of data packets when the sensor is touched. The
controller sends the data as long as a touch continues on the sensor.
Because Mode Stream sends touch data continually, it is the most versatile mode, and it
provides the best response time and overall feel.
3M Touch Systems recommends that the touch driver generate an interrupt as each
packet in the data stream arrives. Because touchdown and liftoff events are specially
coded, your software can generate mouse events that correspond to what the user is
doing. This enables instant feedback and prevents data loss.
Communicating with the Controller
This section provides information on sending firmware commands to the controller and
interpreting the responses that the controller returns.
The commands listed in Table 17 are those that 3M Touch Systems currently uses for
development. 3M Touch Systems recommends that you use only these commands for
3M™ PX serial controller development.
Commands to the controller are sent on the signal Receive Data (RXD) line as a serial
data stream. For each command it receives, the controller sends a response to the host on
the signal Transmit Data (TXD) line also as a serial data stream.