MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 23

• Manufacturer Part Number: MPR121_10
• Description: Proximity Capactive touch Senosr controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

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Freescale Semiconductor
sured, as discussed in AN3889. The FFI sets the number of samples being measured. The result of an FFI setting of 6 or 0x00
would be to take 6 samples, toss the maximum and minimum, then average the remaining 4 samples. The results of an oscillo-
scope output on an electrode with the setting of FFI = 0x00 and CDT is shown in
this example anywhere from 1 ms to 128 ms. Then a value can be selected for how many samples should be averaged.
FILTER CONFIGURATION REGISTER
The properties of the filter are determined by these two settings, but the CDT is determined by the capacitance being mea-
The first level of filtering delivers data to a second filter stage. The second filter stage averages samples over more time, in
Table 20. AFE Configuration Register Field Descriptions
Reset:
CDT
1 μs
Field
CDC
FFI
7:6
5:0
W
R
1
7
0
2 μs
= Unimplemented
First Filter Iterations – The first filter iterations field selects the number of samples
taken as input to the first level of filtering.
00 Encoding 0 – Sets samples taken to 6
01 Encoding 1 – Sets samples taken to 10
10 Encoding 2 – Sets samples taken to 18
11 Encoding 3 – Sets samples taken to 34
Charge Discharge Current – The Charge Discharge Current field selects the supply
current to be used when charging and discharging an electrode.
000000 Encoding 0 – Disables Electrode Charging
000001 Encoding 1 – Sets the current to 1μA
~
111111 Encoding 63 – Sets the current to 63 μA
CDT
2
6
0
Figure 21. Filter Configuration Register
4 μs
5
0
3
Figure 20.
TIME
6 μs
4
0
FFI
SFI
Description
4
3
0
8 μs
Figure
2
0
20.
5
10 μs
ESI
1
0
6
0
0
12 μs
MPR121
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