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Chapter 22
Touchscreen Controller/Analog-to-Digital Converter
The analog signal processor (ASP) may be configured as a touchscreen controller or an analog-to-digital
converter (ADC). As a touchscreen controller, it supports resistive 4-, 5-, 7-, and 8-wire interface touch
panels. When a touchscreen interface is not needed, this module can be used as a multi-channel 12-bit
general purpose ADC.
Figure 22-1
shows the block diagram of the touchscreen/ADC module.
Bus Clock
(f
sys/2
22.1
Overview
The ASP module is composed of an ADC, clock generator, ASP and ADC control blocks, pen-detect logic,
FIFO memory, and bus interface.
•
The ADC block includes the bias network and touchscreen pen-state detection.
•
ADC control works together with the ADC to implement the ADC function.
•
Clock generator generates the programmable ADC_CLK clock from the free-running peripheral
bus clock.
•
ASP control is the core touchscreen control block. It is responsible for running the touchscreen in
the defined sequence according to the operating modes and timing settings.
•
The pen detect block provides pen-down and pen-up interrupts by sampling the pen state signal
from the ADC block and removing the bouncing effect.
•
The FIFO temporarily stores the measured data and allows the MCU to burst the measured data by
using the various FIFO usage flags.
Freescale Semiconductor
Clock
)
Generator
Pen
Detect
ADC +
Bias Network +
Pen State
Figure 22-1. ASP System Block Diagram
MCF52277 Reference Manual, Rev. 1
Internal Bus
Bus Interface
ASP
Control
FIFO
ADC
Control
22-1
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