42.4.5 Scan times
The TSI provides multi-scan function. The number of scans is indicated by the
TSI_GENCS[NSCN] bits that allow the scan number from 1 to 32. When
TSI_GENCS[NSCN] is set to 0 (only once), the single scan is engaged. The 16-bit
counter accumulates all scan results until the NSCN time scan completes, and users can
read TSI_DATA[TSICNT] to get this accumulation. When DMA transfer is enabled, the
counter values can also be read out by DMA engine.
42.4.6 Clock setting
TSI is built with dual oscillator architecture. In normal sensing application, the reference
oscillator clock is the only clock source for operations. The reference clock is used to
measure the electrode oscillator by ticking a 16-bit counter. The reference oscillator
frequency depends on the current source setting. Please refer to the Current source for
more details.
The output of electrode oscillator has several prescalers up to 128 indicated by
TSI_GENCS[PS]bits. This allows a flexible counter configuration for different electrode
oscillator frequency.
42.4.7 Reference voltage
The TSI module offers a internal reference voltage for both electrode oscillator and
reference oscillator. The internal reference voltage can work in low power modes even
when the MCU regulator is partially powered down, which is ideally for low-power touch
detection.
The charge and discharge difference voltage is configurable upon the setting of
TSI_GENCS[DVOLT] bits. The following table shows the all the delta voltage
configurations.Note this table doesn't apply to noise mode, where the details should be
consult form noise modes chapters.
Table 42-11. Delta voltage configuration
DVOLT V
p
(V) V
m
(V) ΔV (V)
00 1.328 0.302 1.026
01 1.111 0.519 0.592
10 0.986 0.644 0.342
11 0.914 0.716 0.198
Functional description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
798 Freescale Semiconductor, Inc.
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