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6.3 USB-MODEVM Interface Board
The simple diagram shown in Figure 1 shows only the basic features of the USB-MODEVM interface
board. The board is built around a TAS1020B streaming audio USB controller with an 8051-based core.
The board features two positions for modular EVMs, or one double-wide serial modular EVM may be
installed.
For use with the TSC2008, the TSC2008EVM is installed in the topmost EVM slot, which connects the
TSC2008 digital control interface to the SP1 port, realized using the TAS1020B. Because the TSC2008
has no audio features, the lower EVM slot, which is connected to the TAS1020B digital audio interface, is
not used.
As configured from the factory, the board is ready to use with the TSC2008EVM.
6.4 Program Description
After the TSC2008EVM-PDK software installation (described in Section 6.2), evaluation and development
with the TSC2008 can begin.
6.4.1 Touch Screen Functions Panel
The touch screen box in this panel is updated when a touch is detected on the touch screen. As the touch
screen is drawn on, the motion on the touch screen is translated into pixels on this box. The software
takes X, Y, and Z readings which are shown to the right of the touch screen box. As the touch pressure is
increased, the pixel size increases; a lighter touch results in smaller pixel sizes.
The Z-value displayed is not what is described in the TSC2008 data sheet, because in the data sheet
equation, it is assumed that the sheet resistance of the touch screen being used is known. The value used
in this program is calculated by Equation 2 of the TSC2008 data sheet, but without multiplying it by the
R
X-plate
resistance. This value ranges from 0 to 3, and larger, with larger numbers representing a more
forceful press on the screen. Using the Maximum Z Value to Display knob, you can set a threshold so
that the program does not display lightly pressed points. This threshold setting helps to eliminate display
of spurious points that may result from touch screen mechanical bouncing.
The display can be cleared by pressing the Clear Graph button on the screen.
6.4.2 Data Acquisition Functions Panel
The TSC2008 has provision for measuring one auxiliary input voltages (AUX) and temperature. This panel
displays the measured values for these parameters. Measurements are updated only when the touch
screen is not being pressed.
Temperature is displayed using both methods described in the TSC2008 data sheet. Using the TEMP0
and TEMP1 measurements, a temperature reading with 2°C resolution and accuracy is achieved. Using
only the TEMP0 measurement, a reading with 0.3°C resolution is possible, but this option requires
knowing the TEMP0 value at +25°C; this normally is a calibration that the user performs. This program
assumes that TEMP0 = 600 mV at +25°C.
6.4.3 Configuration Panel
The TSC2008 can be configured to operate in 8-bit or 12-bit resolution modes. Control over the mode
used is selected in this panel.
Touch screen measurements can be made in either single-ended or differential mode; see the TSC2008
data sheet for a discussion of these modes. The touch screen measurement mode can also be selected in
this panel. If single-ended mode is used, an external reference is highly recommended; however,
single-ended measurements are discouraged for touch screen use because differential mode yields far
more accurate results.
The two power-down bits of the TSC2008 can be set from this panel as well. A brief description of the
mode selected is shown on the screen when setting these bits; see Table 3 (Command Byte Definitions)
of the TSC2008 data sheet (SBAS406) for details on what these bits do.
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TSC2008EVM and TSC2008EVM-PDK User's Guide SLAU248–May 2008
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