NXP Semiconductors KE17Z Series, Руководство пользователя, Страница: 12 / 37

Table 7. TSI_SSC0[SSC_MODE] = 01, up-down counter mode (continued)
Variable Register Clock cycle Description
t3 TSI_SSC0[CHARGE_NUM] 1 ~ 16 SSCLowWidth
There is an example of the advance clock generation attached below.
To use PRBS mode SSC switching clock with central frequency of 1 MHz.
• Set SETCLK<1:0> to ‘01b’ to get main clock = 16.65 MHz.
• Set SSC_PRESCALE_NUM<7:0> to ‘0b’ to get division 1. The divided main clock is 16.65 MHz.
• Set SSC_MODE<1:0> to ‘00b’ to enable PRBS SSC mode. SSC t2 is random.
• Set BASE_NOCHARGE_NUM<3:0> to ‘0100b’ to set t1 = 5. The basic length of SSC output bit 1’s period is five clock
cycle of the divided main clock.
• Set PRBS_OUTSEL<3:0> to ‘0110b’ to set t2 range from 1 to 6. The average of t2 is 3.5. t2 is the random length of SSC
output bit 1’s period. It is 3.5 clock cycle of the divided main clock.
• Set CHARGE_NUM<3:0> to ‘0110b’ to set t3 = 7. The basic length of SSC output bit 1’s period is seven clock cycle of the
divided main clock.
• Keep other registers in TSIx_SSC0, TSIx_SSC1, and TSIx_SSC2 as default value.
• Then, switching clock = 16.65 MHz/[(5+3.5+7) * (0 + 1)] = 1.074 MHz. Switching clock is spectrum spread pulse.
Switcℎing Clock
=
Main Clock
SSC_PRESCALE_NUM + 1 × SSCHigℎWidtℎ t1 + SSCHigℎRandomWidtℎ t2 + SSCLowWidtℎ t3
=
16.65MHz
0 + 1 × 5 + 3.5 + 7 = 1.074MHz
2.4 TSI scan time and scan result accumulation
TSI supports multiple scans per channel. That is, to get better Signal-to-Noise Ratio (SNR) and resolution, TSI performs multiple
scans. The final scan result is accumulated in TSI_DATA[TSICNT] counter as the NSTEP multiplied by number of scans, and the
scan time is multiple of single TSI scan time.
With higher Decimation, the number of scans is increased. The result is the physically longer TSI counter
accumulation and increased resolution.
If the Order is higher than 1, then the scan number physically executed by TSI is smaller than the scan number
calculated by HW. It is beneficial to get the higher resolution.
NOTE
2.4.1 TSI single scan process
Figure 11 shows one process that the step voltage (V
ci
) reaches threshold V
p
of comparator from V
m
. If V
ci
reaches the threshold
V
p
, the voltage VCI is discharged to V
m
for next scanning. The step voltage (V
ci
) depends on touch sensor and IP configuration.
NXP Semiconductors
TSI self-cap mode introduction
KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022
User Guide 12 / 37