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Figure 48-4. Brief timing of TSI operation
Formula
where:
DECIMATION: the times of scan, defined by IP configuration DECIMATION<4:0>.
ORDER: the order of sum up, defined by IP configuration ORDER.
NSTEP: the analog integration steps, decided by IP configurations and sensor.
TNSTEP: the scan time of getting each NSTEP.
SCANTIME: the total scan time of getting each TSICNT.
Operation
• TSI needs very short initialization time for each trigger, then starts to scan touch
sensor.
• During scanning, analog front end senses self-cap/mutual-cap value and generates
voltage steps on integration capacitor. The step voltage depends on touch sensor and
IP configuration.
• Once the step voltage (VCI) reach threshold Vp of comparator, the integration cap
and analog front end will be reset. The voltage VCI is discharged to Vm for next
scanning.
• For each TSI trigger, there are many scan times which is set by registers. The step
numbers of each scan are summed up together as final counts for software to use.
• The counts relate with touch sensor capacitance (self-cap/mutual-cap) through
formulas and it can be used to sense touch event.
Chapter 48 Touch Sensing Input (TSI)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors
1299
Summary of Contents for Kinetis KE1xZ256
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