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51.7.3.4.4 Over-run interrupt
If an electrode scan is in progress and there is a scan trigger, the electrode scan unit
generates and over-run error by asserting GENCS[OVRF]. If the TSI error interrupt is
active by setting GENCS[ERIE], an interrupt request is asserted. The OVRF flag is
cleared by writing 1 to it.
51.7.4 Touch detection unit
The touch detection unit is responsible for detecting electrode capacitance changes while
in low-power mode.
It also detects the occurrence of error with the electrode in the case it capacitance result is
0x0000 or 0xFFFF. The errors can be caused by electrode pin short circuit to V
DD
or V
SS
,
or by electrode capacitances out of the configuration range of the TSI module.
51.7.4.1 Capacitance change threshold
Each TSI pin has the result register TSICHnCNT. In low-power mode, only one electrode
can be active. At the end of the low-power active electrode conversion, the touch
detection unit compares whether the TSICHnCNT result value is within a configurable
range. The comparison range is defined by individual registers: TSICHHTH, the upper
threshold value, and TSICHLTH, the lower threshold value. If TSICHnCNT happens to
be out of the range defined by TSICHLTH and TSICHHTH, the GENCS[OUTRGF] flag
is set indicating that a capacitance change occurred in the low-power active electrode..
51.7.4.1.1 Out-of-range interrupt
The Out-of-range interrupt is used to wake the CPU from low power modes.
The GENCS[OUTRGF] flag generates a TSI interrupt request if GENCS[TSIIE] is set
and GENCS[ESOR] is cleared. With this configuration, after the end-of-electrode scan,
the TSI interrupt is requested only when there is a capacitance change. If the low-power
electrode capacitance does not vary, the TSI Interrupt does not interrupt the CPU.
51.7.4.2 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.
Chapter 51 Touch sense input (TSI)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1435
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