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CHAPTER 19 PIU (TOUCH PANEL INTERFACE UNIT)
This chapter explains the operation of the PIU and how to set the registers of the PIU.
19.1 GENERAL
The PIU detects the X and Y coordinates of the point where the pen is touched to the panel by using
an external A/D converter. As a secondary function, it also measures the battery voltage. As the
external A/D converter, the TI TLV1543C (conversion accuracy: 10 bits) and TLC2543C (conversion
accuracy: 12 bits) are supported.
The functions of the PIU such as the detection of the X and Y coordinates on the panel and the
measurement of battery voltage are implemented as follows:
Hardware functions:
Control of the external circuit
Acceptance of coordinate/battery voltage data and data transfer.
Software functions: Processing of coordinate/battery voltage data based on the data sampled by
hardware
Features of the hardware portion of the PIU are as follows:
I/F dedicated to touch panel based on 4-terminal-type resistance films
I/F dedicated to two types of A/D converters (TC2543C and TLV1543C made by TI, Inc.)
Main/sub battery voltage detection
Control of the A/D converter and external circuit by arbitrary setting
X and Y coordinate data and pen pressure data sampling
Variable interval of coordinate data sampling
Variable clock cycle for the A/D converter
Generation of interrupts by pen touch
DMA channel dedicated for the PIU
Auto/manual is selectable for coordinate data sampling start/stop control