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6.4 Program Description
Kit Operation
As configured from the factory, the board is ready to use with the ADS7845EVM. However, if external SPI
control is desired, the signals may be applied to J15, as long as the SW2 is set so that USB SPI control is
disabled. To view all the functions and configuration options available on this board, see the
USB-MODEVM Interface Board schematic in Section 7.2 .
After the ADS7845EVM-PDK software installation (described in Section 6.2 ), evaluation and development
with the ADS7845 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 and Y readings which are shown to the right of the touch screen box.
The display can be cleared by pressing the Clear Graph button on the screen.
6.4.2 Data Acquisition Functions Panel
The ADS7845 provides for measuring an auxiliary input voltage. A data acquisition functions panel
displays the measured value for this parameter. Measurements are updated only when the touch screen is
not being pressed. Note that these measurements depend on the reference voltage and are affected by
the setting of the power-down bits. The software presumes that the reference voltage is 2.5V.
6.4.3 Configuration Panel
The ADS7845 can be configured to operate in either 8-bit or 12-bit resolution mode. This panel controls
the mode selection.
Touch screen measurements may be made in either single-ended or differential mode; see the ADS7845
data sheet for a discussion of these modes. The touch screen measurement mode may also be selected
in this panel. If single-ended mode is used, ensure that a reference voltage is supplied; 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 ADS7845 can also be set from this panel. A brief description of the mode
selected is shown on the screen when setting these bits; see Table V of the ADS7845 data sheet for
details on the functions of these bits.
6.4.4 Datalogging
The software can record the data it is taking from the ADS7845 to a tab-delimited file, suitable for
importing into spreadsheets. To do this, first go into the File menu, and select Log Data to File..., which
opens a file-select window and allows you to specify a file to which to write the data. At the same time,
this feature enables the Datalogging menu.
When ready to begin recording data to a file, select Datalogging → Start Logging. Data is written to the file
until Datalogging → Stop Logging is selected. When the screen is not touched, the AUX values are written
to the file, and the X and Y parameters are written to the file with values of 9999, to indicate that they are
not updated. When the screen is touched, the X and Y parameters are written while the AUX values are
written to the file as 9999. Because the program constantly updates at a rate of about 400 readings per
second, datalog files can quickly grow large; therefore, log only what is necessary.
The format of the data file has the first column as the time in milliseconds (just a timer in the program,
which can arbitrarily start at any number), then X, Y, and AUX columns. Every new reading is a new row
in the file.
SBAU122 – March 2006 ADS7845EVM and ADS7845EVM-PDK 9
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