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51.7.3.2 Scan trigger
The scan trigger can be set to periodical scan or software trigger. GENCS[STM]
determines the TSI scan trigger mode. If STM = 1, the trigger mode is selected as
continuous. If STM = 0, the software trigger mode is selected. In periodic mode, the scan
trigger is generated automatically by the electrode scan unit
51.7.3.3 Software trigger mode
The software trigger scan is started by writing 1 to the bit GENCS[SWTS]. A single scan
of all active electrodes is performed. The software trigger scan can be initiated only by
the GENCS[SWTS] bit if the STM = 0. If STM = 1, any write in the GENCS[SWTS] bit
is ignored.
51.7.3.4 Periodic scan control
The electrode scan unit operates both in TSI active mode and TSI low-power mode. It has
a separate scan period control for each one of these modes. It allows the application to
controls the trade-off of the scan frequency and the average TSI module power
consumption.
SMOD
SMOD SMOD
Periodic Scan
Trigger
Periodic Scan
Trigger
Periodic Scan
Trigger
Periodic Scan
Trigger
E1
E1
E1
E1
E2
E2 E2
En
En
En
...
...
...
...
Time
Figure 51-40. Periodical scan time chart
51.7.3.4.1 Active mode periodic scan
In active mode periodic scan the scan following clocks can be selected: LPOOSCCLK,
MCGIRCLK, and OSCERCLK. The field SCANC[AMCLKS] selects the TSI clock
source for the active mode scan. The scan period is determined by the SCANC[SMOD]
value. SMOD is the module of the counter that determines the scan period.
The following figure presents the scan sequence performed by the TSI module. Every
active electrode is scanned sequentially, starting with the TSI_IN[0] and ending with the
TSI_IN[15] pin, if they are active.
Chapter 51 Touch sense input (TSI)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1433
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