K60P100M100SF2RM Datasheet, PDF (1785/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 55 Touch sense input (TSI)
When GENCS[OUTRGF] flag is asserted, it is requested the software to poll which
specific electrode is out of range by reading the status from STATUS register, clearing
the corresponding electrodes flags will also clear the out-of-range flag in
GENCS[OUTRGF].
55.7.4.2 Error interrupt
The GENCS[EXTERF] is set in the case the capacitance result registers, TSICHnCNT, of
a TSI pin is either 0 or 0xFFFF, the two possible extreme values. The EXTERF flag
generates a TSI Error Interrupt request if the GENCS[ERIE] bit is set.
When the GENCS[EXTERF] is set, the registers STATUS register indicates which TSI
pins have the error condition by setting the correspondent STATUS[ERRORx] bit.
Before clearing the error flags, users need to check which channel is problematic and
then clear the corrersponding flags in STATUS register.
55.8 Application information
After enabling the TSI module for the first time, it is highly recommended to calibrate all
the enabled channels by setting proper high and low threshold value for each active
channel. All the channel dedicated counter values can be read from each counter value
registers. The software suite can then adjust the threshold based on these values.
Follow proper PCB layout guidelines for board design on electrode shapes, sizes, routes,
etc. Visit http://www.freescale.com/touch for application notes and reference designs.
55.8.1 TSI module sensitivity
The TSI module sensitivity is defined by the increment in the two 16-bit TSICHnCNT
result registers caused by a reference capacitor value 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 =1 µA, the
TSI_sensitivity = 64 count/pF
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1785