MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 26

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

MPR121
26
AN3891: MPR121 Baseline System
INTRODUCTION
tightly coupled. The purpose of the baseline filter is to “filter out touches” resulting in a system that is similar to a long term
average but also takes into account that one specific signature. A touch must have different properties than noise and
environmental change with respect to the filter response. This is accomplished through four register types that operate under
different conditions. These are Max Half Delta (MHD), Noise Half Delta (NHD), Noise Count Limit (NCL) and Filter Delay Limit
(FDL).
MAX HALF DELTA (NHD)
Touch acquisition takes a few different parts of the system in order to detect touch. The baseline filter and touch detection are
Table 22. Max Half Delta Register Field Descriptions
Reset:
Field
MHD
AFE AQUISITION
5:0
W
R
1 - 32 μs
DATA
RAW
7
0
0
= Unimplemented
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
6
0
0
Figure 24. Data Flow in the MPR121
1 - 128 μs
FILTER
1st
5
0
4
0
FILTER
2nd
Description
4 - 2048 μs
3
0
STATUS REGISTER
MHD
TOUCH
IRQ
2
0
BASELINE
FILTER
1
0
Freescale Semiconductor
0
0
Sensors