Communicating With The Controller - 3M SC400 Reference Manual

16
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 operating mode for the SC400 controller. In Mode Stream, the
controller sends a continuous stream of data packets when the screen is touched. The
controller sends the data as long as a touch continues on the touch screen.
Mode Stream provides the best response time and overall feel.
3M Touch Systems recommends that the touch screen driver generate an interrupt as each
packet in the data stream arrives. Because touchdown and liftoff events are specially
coded, provided that the interrupts are sent as recommended, your software always knows
exactly 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 responses.
The commands listed in Table 3 are those that 3M Touch Systems currently uses for
development and recommends that you use only these commands.
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.
Sending Commands to the Controller
When you send a command to the controller, you must use the correct command format.
The general format of a command is as follows:
<Header>Command<Terminator>
Note: The following descriptions of header, command, and terminator, use 3M Touch Systems
terminal emulator key sequences. You may need to enter the sequence in a different format,
depending on your emulator.
The header is the first character in the command string and is the ASCII start-of-header
control character SOH. The hexadecimal code for the ASCII SOH control character is 01.
To start the command sequence, use the key combination Ctrl A (^A). If you are working
with an IBM PC compatible system, the Ctrl A key combination immediately returns an
ASCII ☺ character.
The command, which always follows the header, consists of ASCII uppercase letters and
numbers only (printable characters).
3M Touch Systems Proprietary Information
SC400 Controller Reference Guide