K60P100M100SF2RM Datasheet, PDF (1777/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 55 Touch sense input (TSI)
55.6.6 Channel n threshold register (TSIx_THRESHLD)
All THRESHLD bits can be read at any time, but must not be written while
GENCS[SCNIP] is set.
Addresses: 4004_5000h base + 120h offset + (4d × n), where n = 0d to 15d
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
R
LTHH
W
HTHH
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
TSIx_THRESHLDn field descriptions
Field
31–16
LTHH
15–0
HTHH
Low threshold value
High threshold value
Description
55.7 Functional descriptions
This section provides functional description of the TSI module.
55.7.1 Capacitance measurement
The electrode pin capacitance measurement uses a dual oscillator approach. The TSI
electrode oscillator has its frequency dependable on the external electrode capacitance
and the TSI module configuration. After going to a configurable prescaler, the TSI
electrode oscillator signal goes to the input of the modulo counter. The time for the
external electrode oscillations is measured using the TSI reference oscillator. The
measured electrode capacitance is directly proportional to this time.
55.7.1.1 TSI electrode oscillator
The TSI electrode oscillator circuit is illustrated in the following figure. A configurable
constant current source is used to charge and discharge the external electrode
capacitance. A buffer hysteresis defines the oscillator delta voltage. The delta voltage
defines the margin of high and low voltage which are the reference input of the
comparator in different time.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1777