Texas Instruments TSC2007EVM - Manual (Page 8)

www.ti.com
6.3 USB-MODEVM Interface Board
6.4 Program Description
6.4.1 Touch Screen Functions Panel
6.4.2 Data Acquisition Functions Panel
6.4.3 Configuration Panel
Kit Operation
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 TSC2007, the TSC2007EVM is installed in the topmost EVM slot, which connects the
TSC2007 digital control interface to the I
2 C port, realized using the TAS1020B. Because the TSC2007 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 TSC2007EVM except for SW2, in which
case at least one of SW2-1, SW2-2, and SW2-3 must be set to OFF.
After the TSC2007EVM-PDK software installation (described in Section 6.2 ), evaluation and development
with the TSC2007 can begin.
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 TSC2007 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 TSC2007 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.
The TSC2007 has provision for measuring one auxiliary input voltages (AUX1) 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 TSC2007 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 would normally be a calibration that the user would perform. This
program assumes that TEMP0 = 600 mV at +25°C.
The TSC2007 can be configured to operate in 8-bit or 12-bit resolution modes. Control over the mode
used is selected in this panel.
In the middle of this panel is an indicator light that shows the I 2 C Bus Status. If the TSC2007 is
acknowledging the address sent, the light is green; if the TSC2007 cannot acknowledge, the light is red.
The address to which the TSC2007 is set is shown in binary format in the box labeled Device Address
A1-A0. The address set here should be "00" when using the TSC2007EVM. Even though the TSC2007
has two pins, A0 and A1, for users to select four different I2C addresses, the TSC2007EVm has only a
fixed address 1001000b, where A0=A1="0", because both A0 and A1 are tied to ground. See the
TCS2007EVM schematic provided in this document.
8 TSC2007EVM and TSC2007EVM-PDK User's Guide SLAU199 – March 2007
Submit Documentation Feedback