CHAPTER 14 TOUCH PANEL INTERFACE UNIT (PIU)
User’s Manual U14272EJ3V0UM
276
14.1.1 Block diagrams
Figure 14-1. PIU Peripheral Block Diagram
V
R
4181
Battery, etc.
I/O
Buffer
I/O
Buffer
PIU
ADC
Selector
4
AIU
AUDIOIN
ADIN2
ADIN1
ADIN0
TPY1
TPY0
TPX1
TPX0
Touch panel
4
1
• Touch panel
A set of four pins are located at the edges of the X-axis and Y-axis resistance layers, and the two layers have
high resistance when there is no pen contact and low resistance when there is a pen contact. The resistance
between the two edges of the resistance layers is about 1 k
Ω
. When a voltage is applied to both edges of the
Y-axis resistance layer, the voltage (V
Y1
and V
Y2
in the figure below) is measures at the X-axis resistance
layer’s pins to determine the Y coordinate. Similarly, when a voltage is applied to both edges of the X-axis
resistance layer, the voltage (V
X1
and V
X2
in the figure below) is measures at the Y-axis resistance layer’s pins
to determine the X coordinate. For greater precision, voltages are again measured after switching plus and
minus of the voltage applied to the resistance layer’s pins. The obtained data is stored into the PIUPBnmREG
register (n = 0 or 1, m = 0 to 3).