NXP Semiconductors MKW01Z128, Reference Manual

Page: 837 / 884

7. Check whether the TSI counter value is within the given counter window
(WINDOW, can be 2 or 3 or 5): If the TSI counter value < WINDOW (i.e., the noise
level is detected), go to step 12; Otherwise continue with the next step (meaning the
noise level is too large);
8. If (Rs = minimum value) (i.e., TSI_CS2[EXTCHRG] =000b, noise level is the
largest at given DVOLT), go to step 10; otherwise continue with the next step;
9. Reduce Rs value by incrementing TSI_CS2[EXTCHRG] by 1 and then go to step 4;
(This action detects the next high level of noise)
10. If (DVOLT = maximum value) ( i.e., TSI_CS2[DVOLT] =00b), this means noise is
too large to detect, go to END; otherwise continue with the next step;
11. Increase DVOLT to the next level by decrementing TSI_CS2[DVOLT] by 1 and set
Rs to the max value, then go to step 4; (It means noise level is higher, so need find
high DVOLT)
12. Reduce Rs value by incrementing TSI_CS2[EXTCHRG] by 1 if (Rs > minimum
value) (i.e., TSI_CS2[EXTCHRG] < 111b), and then go to END (Now a matching
DVOLT corresponding to the noise level is found)
13. Reduce DVOLT by incrementing TSI_CS2[DVOLT] by 1 if (Rs = maximum value)
(i.e.,TSI_CS2[EXTCHRG] = 011b); (Now a matching DVOLT corresponding to the
noise level is found)
14. END:
NOTE
The END condition of above algorithm can be one of
• TSI counter value within the WINDOW and Rs ≥ minimum
value
• TSI counter value out of the WINDOW and Rs = minimum
value and DVOLT = maximum value
At the end of the above steps, the correct matching DVOLT value and the electrode
oscillator charge and discharge current value for the current noise level is found. That is,
the correct TSI_CS2[DVOLT] value and TSI_CS2[EXTCHRG] value are found for the
current noise level. And now users can proceed with normal capacitive sense procedure
by keeping both TSI_CS[DVOLT] and TSI_CS2[EXTCHRG] untouched, that is, users
just need switch to normal capacitive sense mode by clearing
TSI_CS3[STAT_STUP[3:2]] bits and start TSI scan.
For typical applications, the noise detection/sense algorithm shall be performed first
followed by normal capacitive sense for a given channel and then alternate between noise
sense and capacitive sense as shown in
Figure 35-7 .
Noise
sense
Capacitive
sense
Noise
sense
Figure 35-7. Noise detection/sense algorithm of typical application
Functional description
MKW01Z128 MCU Reference Manual, Rev. 3, 04/2016
706 Freescale Semiconductor, Inc.