MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 33

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

Sensors
Freescale Semiconductor
AN3892: MPR121 Jitter and False Touch Detection
INTRODUCTION
tightly coupled. The purpose of the touch detection block is to use the baseline value and the 2nd level filter data to determine
when a user has touched an electrode. The electrodes are independently configured using the Touch Threshold and Release
Threshold registers. The global Debounce register also controls when a touch is detected by adding some minimal delay. The
data is then output through a couple of registers: Filtered Data High, Filtered Data Low, Baseline Data and two touch output reg-
isters.
two registers in the map. The two touch status registers both trigger an interrupt on any change of the data. Thus, as a touch
happens (bit is set) an interrupt will be triggered, and when a touch is released (bit is cleared) it will also trigger. To clear the
interrupt all you must do is initiate a I2C communication, with the intent that you read register 0x00 and 0x01 to determine which
electrodes are touched.
Touch acquisition takes a few different parts of the system in order to detect touch. The baseline filter and touch detection are
First, the MPR121 touch sensor detects touch by the methods in this application note, and the data is output through the first
AFE AQUISITION
1 - 32 μs
DATA
RAW
Figure 37. Data Flow in the MPR121
1 - 128 μs
FILTER
1st
FILTER
2nd
4 - 2048 μs
STATUS REGISTER
TOUCH
IRQ
BASELINE
FILTER
MPR121
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