Freescale Semiconductor Evaluation Board MPR031/2 for 2- or 3-pad touch sensor controllers DEMOMPR031 DEMOMPR031 データシート
製品コード
DEMOMPR031
MPR03X
Sensors
Freescale Semiconductor
Freescale Semiconductor
21
8.4
Third Level Filter
The Third Level Filter is designed for varying implementations. It can be used as either an additional low pass filter for the
electrode data or a baseline for touch detection. For it to function as a baseline filter, it must be used in conjunction with the touch
detection system described in the next chapter. To use the filter as an additional layer for low pass filtering, the touch detection
system must be disabled by setting all of the touch thresholds to zero (refer to
electrode data or a baseline for touch detection. For it to function as a baseline filter, it must be used in conjunction with the touch
detection system described in the next chapter. To use the filter as an additional layer for low pass filtering, the touch detection
system must be disabled by setting all of the touch thresholds to zero (refer to
). Although, in most cases the third
level of filter will be used as a baseline filter. The primary difference between these implementations is this: if a touch is detected
the baseline filter will hold its current value until the touch is released. The touch/release configuration will be described in
the baseline filter will hold its current value until the touch is released. The touch/release configuration will be described in
When a touch is not currently detected, the baseline filter will operate based on a few conditions. These are configured through
a set of registers including the Max Half Delta Register, the Noise Half Delta Register, and the Noise Count Limit.
a set of registers including the Max Half Delta Register, the Noise Half Delta Register, and the Noise Count Limit.
8.4.1
The Max Half Delta register is used to set the Max Half Delta for the Third Level Filter. The address of the Max Half Delta Register
is 0x26.
is 0x26.
Figure 27. Max Half Delta Register
Table 13. Filter Configuration Register Field Descriptions
Field
Description
7:5
CDT
Charge Discharge Time – The Charge Discharge Time field selects the amount
of time an electrode charges and discharges.
000 Encoding 0 – Invalid
001 Encoding 1 – Time is set to 0.5
of time an electrode charges and discharges.
000 Encoding 0 – Invalid
001 Encoding 1 – Time is set to 0.5
s
010 Encoding 2 – Time is set to 1
s
~
111 Encoding 7 – Time is set to 32
111 Encoding 7 – Time is set to 32
s.
4:3
SFI
Second Filter Iterations – The Second Filter Iterations field selects the number of
samples taken for the second level filter.
00 Encoding 0 – Number of samples is set to 4
01 Encoding 1 – Number of samples is set to 6
10 Encoding 2 – Number of samples is set to 10
11 Encoding 3 – Number of samples is set to 18
samples taken for the second level filter.
00 Encoding 0 – Number of samples is set to 4
01 Encoding 1 – Number of samples is set to 6
10 Encoding 2 – Number of samples is set to 10
11 Encoding 3 – Number of samples is set to 18
2:0
ESI
Electrode Sample Interval – The Electrode Sample Interval field selects the
period between samples used for the second level of filtering.
000 Encoding 0 – Period set to 1 ms
001 Encoding 1 – Period set to 2 ms
~
111 Encoding 7 – Period set to 128 ms
period between samples used for the second level of filtering.
000 Encoding 0 – Period set to 1 ms
001 Encoding 1 – Period set to 2 ms
~
111 Encoding 7 – Period set to 128 ms
7
6
5
4
3
2
1
0
R
0
0
MHD
W
Reset:
0
0
0
0
0
0
0
0
= Unimplemented
Table 14. Max Half Delta Register Field Descriptions
Field
Description
5:0
MHD
Max Half Delta – The Max Half Delta determines the largest magnitude of
variation to pass through the third level filter.
000000 DO NOT USE THIS CODE
000001 Encoding 1 – Sets the Max Half Delta to 1
~
111111 Encoding 63 – Sets the Max Half Delta to 63
variation to pass through the third level filter.
000000 DO NOT USE THIS CODE
000001 Encoding 1 – Sets the Max Half Delta to 1
~
111111 Encoding 63 – Sets the Max Half Delta to 63