Information

Only one electrode pin is functional in the low power mode scan and it’s defined by the
bit-field PEN[LPSP]. In low power scan mode the configuration of PEN[PEN] bits are
ignored.
48.7.3.2 Scan trigger
The scan trigger can be set to periodical scan or software trigger. The bit 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
48.7.3.3 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 only can be initiated by
the GENCS[SWTS] bit if the STM = 0. If STM = 1, any write in the GENCS[SWTS] bit
is ignored.
48.7.3.4 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 48-40. Periodical Scan Time Chart
Chapter 48 Touch sense input (TSI)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 1209