CP3BT23_14 Datasheet, PDF (111/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
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SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
16.2 TOUCHSCREEN INTERFACE
The ADC provides an interface for 4-wire resistive touchscreens with the resolution necessary for
applications such as signature analysis. A typical touchscreen configuration is shown in Figure 16-2.
Figure 16-2. Touchscreen Interface
A touchscreen consists of two resistive plates normally separated from each other. The TSX+ and
TSXsignals are connected to opposite ends of the X plate, while the TSY+ and TSYsignals are connected
to the Y plate. If the pen is down, the plates will be shorted together at the point of pen contact. The
location of the pen is sensed by driving one end of a plate to VCC, driving the opposite end to ground, and
sensing the voltage at the point of pen contact using the other plate. This is done twice, once for each
coordinate.
An external RC low-pass filter is used to remove noise coupled to the touchscreen signals from the display
drivers.
16.2.1 Touchscreen Driver Configuration
An equivalent circuit for the touchscreen interface is shown in Figure 16-3.
Figure 16-3. Touchscreen Driver Equivalent Circuit
Low-ohmic drivers are provided to pull the TSX+ and TSY+ signals to VCC and the TSXand TSYsignals to
GND. The on-resistance of these drivers is specified to be 6 ohms.
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