Chapter 42
Touch Sensing Input (TSI)
42.1 Introduction
The touch sensing input (TSI) module provides capacitive touch sensing detection with
high sensitivity and enhanced robustness. Each TSI pin implements the capacitive
measurement by a current source scan, charging and discharging the electrode, once or
several times. A reference oscillator ticks the scan time and stores the result in a 16-bit
register when the scan completes. Meanwhile, an interrupt request is submitted to CPU
for post-processing if TSI interrupt is enabled and DMA function is not selected.The TSI
module can be periodically triggered to work in low power mode with ultra-low current
adder and wake CPU at the end of scan or the conversion result is out of the range
specified by TSI threshold. It provides a solid capacitive measurement module to the
implementation of touch keyboard, rotaries and sliders.
42.1.1 Features
TSI features includes:
• Support up to 16 external electrodes
• Automatic detection of electrode capacitance across all operational power modes
• Internal reference oscillator for high-accuracy measurement
• Configurable software or hardware scan trigger
• Fully support Freescale touch sensing software (TSS) library, see
www.freescale.com/touchsensing.
• Capability to wake MCU from low power modes
• Compensate for temperature and supply voltage variations
• High sensitivity change with 16-bit resolution register
• Configurable up to 4096 scan times.
• Support DMA data transfer
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 785
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