TSI software configurations
KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016
10
NXP Semiconductors
There’s an example of the advance clock generation attached below.
PRBS is enabled by setting SSC Mode = 00, then the SSC t2 is random. Setting SSCHighRandomWith
as 6 means the t2 ranges from 1×MainClock to 6×MainClock. As a result, the average t2 is
(1+6)/2=3.5×MainClock.
According to the formula of clock generation, the SwitchingClock = MainClock/(t1+t2+t3) =
16.65/(6+3.5+3) = 1.33MHz
3.1.2. Scan time
The scan time determines how long the TSI finishes the scan and get the conversion result. The typical
single scan time of the self-mode is around 200us, when the TSI acquisition time (switching clock) is
configured as 1us. In order to minimize the noise deviation on the single scan, TSI supports multiple
scan per channel, which means TSI performs scan operation for many times. The final scan result will
be accumulated in TSI_DATA[TSICNT] as the NSTEP of the single scan multiples scan number, and
the scan time will be the scan time of the single scan multiples scan number.
Multiple Scan per Channel
The scan number is configured by TSI_SINC[DECIMATION], [ORDER] and [CUTOFF], which allows
the scan number from 1 to
32
2
. When the decimation is set to 0 (only once), the single scan is engaged.
The 16-bit counter accumulates all scan results until the scan number reaches predefined number, and
users can read TSI_DATA[TSICNT] to get the final scan result.
Variable
Register
Descriptions
t1
TSI_SSC0[BASE_NOCHARGE_NUM]
SSCHighWidth
t2
TSI_SSC0[PRBS_OUTSEL]
SSCHighRandomWidth
t3
TSI_SSC0[CHARGE_NUM]
SSCLowWidth
Main Clock(MHz) SSC Mode SSCHighWidth(t1) SSCHighRandomWidth(t2) SSCLowWidth(t3) Switching Clock(MHz)
16.65
00
6
6
3
1.33
