Information

51.8 Application information
After enabling the TSI module for the first time, calibrate all the enabled channels by
setting proper high and low threshold value for each active channel. All of the channel
dedicated counter values can be read from each counter value register, then the software
suite can adjust the threshold based on these values.
Follow proper PCB layout guidelines for board design on electrode shapes, sizes, routes,
etc. Visit www.freescale.com/touch for application notes and reference designs.
51.8.1 TSI module sensitivity
The TSI module sensitivity is defined by the increment cause in the TSICHnCNT result
registers caused by a 1 pF delta in the electrode pin capacitance.
It is given by the following equation:
TSI
sensitivity
Iref * PS * NSCN
Cref
*
I
For the example provided, I
ref
= 2 µA, PS = 2; NSCN = 16, C
ref
= 1.0 pF and I =2 µA, the
TSI
sensitivity
= 0.03125 pf/count
51.9 TSI module initialization
This section provides the recommended initialization sequence for the TSI module.
Prior to enabling TSI module by setting TSI_GENCS[TSIEN] , you must configure other
bits first. The pin enable registers are set to select which channels will be sampled. The
dual oscillators configuration bits are set to make the scan and conversion more accurate.
Also remember not to change the settings while TSI is working in progress. To switch
from different scan modes, for instance, you must do a software reset to TSI by disabling
and then enabling TSI_GENCS[TSIEN].
51.9.1 Initialization sequence
Freescale TSS library has complete support for TSI, which makes the configuration and
application much easier. For detailed information on how to work with TSI and TSS
together, visit www.freescale.com/touchsensing to get the application notes for details.
Application information
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
1436
Preliminary
Freescale Semiconductor, Inc.
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