Datasheet

720
32142D–06/2013
ATUC64/128/256L3/4U
29.7.3 Resistive Touch Screen Pin Connections
The resistive touch screen film signals connects to the ADCIFB using the AD and ADP pins. The
X
P
(top) and X
M
(bottom) film signals are connected to ADtspo+0 and ADtspo+1 pins, and the Y
P
(right) and Y
M
(left) signals are connected to ADtspo+2 and ADtspo+3 pins. The tspo index is
configurable through the Touch Screen Pin Offset (TSPO) field in the Mode Register (MR) and
allows the user to configure which AD pins to use for resistive touch screen applications. Writing
a zero to the TSPO field instructs the ADCIFB to use AD0 through AD3, where AD0 is con-
nected to X
P
, AD1 is connected to X
M
and so on. Writing a one to the TSPO field instructs the
ADCIFB to use AD1 through AD4 for resistive touch screen sequencing, where AD1 is con-
nected to X
P
and AD0 is free to be used as an ordinary ADC channel.
When the Analog Pin Output Enable (APOE) bit in the Mode Register (MR) is zero, the AD pins
are used to measure input voltage and drive the GND sequences, while the ADP pins are used
to drive the VDD sequences. This arrangement allows the user to reduce the voltage seen at the
AD input pins by inserting external resistors between ADP0 and X
P
and ADP1 and Y
P
signals
which are again directly connected to the AD pins. It is important that the voltages observed at
the AD pins are not higher than the maximum allowed ADC input voltage. See Figure 29-3 on
page 721 for details regarding how to connect the resistive touch screen films to the AD and
ADP pins.
By adding a resistor between ADP0 and X
P
, and ADP1 and Y
P
, the maximum voltage observed
at the AD pins can be controlled by the following voltage divider expressions:
The Rfilmx parameter is the film resistance observed when measuring between X
P
and X
M
. The
Rresistorx parameter is the resistor size inserted between ADP0 and X
P
. The definition of Rfilmy
and Rresistory is the same but for ADP1, Y
P
, and Y
M
instead.
Table 29-2. Resistive Touch Screen Pin Connections
ADCIFB Pin TS Signal, APOE == 0 TS Signal, APOE == 1
ADP0 Xp through a resistor No Connect
ADP1 Yp through a resistor No Connect
ADtspo+0 Xp Xp
ADtspo+1 Xm Xm
ADtspo+2 Yp Yp
ADtspo+3 Ym Ym
VAD
tspo 0+

R
filmx
R
filmx
R
resistorx
+
-------------------------------------------- -
VDP
0
=