![](http://datasheet.mmic.net.cn/100000/IF180C52TXXX-20R_datasheet_3493957/IF180C52TXXX-20R_595.png)
595
32099I–01/2012
AT32UC3L016/32/64
When the sequencer enters the TSPO+0 channel the Resistive Touch Screen Sequencer will
take over control and convert the next 4 channels as described in
Section 26.7.4.
26.7.1
Resistive Touch Screen Principles
A resistive touch screen is based on two resistive films, each one fitted with a pair of electrodes,
placed at the top and bottom on one film, and on the right and left on the other. Between the two,
there is a layer that acts as an insulator, but makes a connection when pressure is applied to the
Figure 26-2. Resistive Touch Screen Position Measurement
26.7.2
Position Measurement Method
to X
P (top) and Xm (bottom) leaving Yp and Ym tristated. Due to the linear resistance of the film,
there is a voltage gradient from top to bottom on the first film. When a contact is performed on
the screen, the voltage at the contact point propagates to the second film. If the input impedance
on the Y
P (right) and Ym (left) electrodes are high enough, no current will flow, allowing the volt-
age at the contact point to be measured at Y
p. The value measured represents the vertical
position component of the contact point.
For the horizontal direction, the same method is used, but by applying voltage from Y
P (right) to
Y
m (left) and measuring at XP.
In an ideal world (linear, with no loss), the vertical position is equal to:
VY
P / VDD
To compensate for some of the real world imperfections, VX
P and VXm can be measured and
used to improve accuracy at the cost of two more conversions per axes. The new expression for
the vertical position then becomes:
(VY
P - VXM) / (VXP - VXM)
XM
XP
YM
YP
XP
XM
YP
VDD
GND
Volt
Horizontal Position Detection
YP
YM
XP
VDD
GND
Volt
Vertical Position Detection
Pen
Contact