T32UC3L0128_14 Datasheet, PDF (613/852 Pages) ATMEL Corporation – Compact Single-cycle RISC Instruction Set Including DSP Instructions

AT32UC3L0128/256
26.7.3 Resistive Touch Screen Pin Connections
Table 26-2. Resistive Touch Screen Pin Connections
ADCIFB Pin
TS Signal, APOE == 0
ADP0
Xp through a resistor
ADP1
Yp through a resistor
ADtspo+0
Xp
ADtspo+1
Xm
ADtspo+2
Yp
ADtspo+3
Ym
TS Signal, APOE == 1
No Connect
No Connect
Xp
Xm
Yp
Ym
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 26-3 on
page 614 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:
VAD_{tspo + 0}=
----------------^R---^f--ⁱ--^l--^m---^x----------------
R_filmx + R_resistorx

VDP₀
32145C–06/2013
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.
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