K60P100M100SF2RM Datasheet, PDF (1782/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional descriptions
55.7.3.2 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.
NOTE
It takes some time (less than 40 µs) for TSI oscillators to be
stable in software trigger mode and periodical scan mode.In the
first scan process, TSI_GENCS[SCNIP] lags some time before
a valid after trigger happens.
55.7.3.3 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.
55.7.3.4 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.
55.7.3.4.1 Active mode periodic scan
In active mode periodic scan the scan following clocks can be selected: BUS_CLK,
MCGIRCLK and OSCERCLK. The bit 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 modulo 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, stating with the TSI_IN[0] and ending with the
TSI_IN[15] pin, if they are active.
When the electrode scan unit starts a scan sequence, all the active electrodes will be
scanned sequentially where each electrode has the scanned time defined by
GENCS[NSCN]. The counter value is the sum of the total scan times of that electrode.
1782
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.