Specifications

Chapter 4 - Smart-Frame Protocol CARROLL TOUCH
4-14 Touch System Programmer’s Guide
Using a baud rate above 2400 baud does not produce any increase in
apparent touch responsiveness. This is due to the fact that the
communication bandwidth required to transmit the four-byte touch
coordinate reports at the typical rate of 30 scans per second is slightly
above 1200 baud. Therefore, using a baud rate above 2400 baud is
unnecessary and merely reduces the noise immunity of the
communication channel while producing no increase in apparent touch
responsiveness.
SFP Timing
The following timing parameters apply to touch systems that use the
Smart-Frame Protocol.
Autobaud/Autoparity Delay Time
During the autobaud/autoparity initialization sequence, a delay of at
least 100 milliseconds must be present between the carriage returns and
after the Software_Reset (3CH) command. This delay is required in
order for the autobaud/autoparity algorithms to work properly.
Maximum Command Completion Time
The maximum amount of time required for a Smart-Frame Protocol
command to be processed and a corresponding report (if any) to be
generated is one second. Touch applications should use at least this
amount of time as their time-out value when awaiting a Smart-Frame
report.
Reset Time/Diagnostics Completion Time
The maximum amount of time required for a touch system that uses the
Smart-Frame Protocol to become ready to begin the autobaud/
autoparity sequence or to receive commands is one second. Touch
applications should either wait at least this amount of time or wait for
some other signal that the touch system is ready to receive commands
(such as the assertion of the Clear To Send (CTS) signal if serial
hardware flow control is used) before beginning the autobaud/
autoparity sequence or sending commands to the touch system.
SFP Programming Examples
The Carroll Touch Driver/Demo Disk contains five short example
programs under the heading of “Programmer’s Guide Programming
Examples.” They demonstrate how to interface directly to
RS-232-based and HBC-based touch systems using the Smart-Frame