Texas Instruments TSC2007EVM USB-MODEVM Interface Board, Program Description, Configuration Panel

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Kit Operation

6.3USB-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 TSC2007, the TSC2007EVM is installed in the topmost EVM slot, which connects the TSC2007 digital control interface to the I2C 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.

6.4Program Description

After the TSC2007EVM-PDK software installation (described in Section 6.2), evaluation and development with the TSC2007 can begin.

6.4.1Touch 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 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

RX-plateresistance. 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.

6.4.2Data Acquisition Functions Panel

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.

6.4.3Configuration Panel

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 I2C 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

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