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
23
9
Touch Detection
9.1
Introduction
The MPR03X uses a threshold based system to determine when touches occur. This section will describe that mechanism.
9.2
Thresholds
When a touch pad is pressed, an increase in capacitance will be generated. The resulting effect will be a reduction in the ADC
counts. When the difference between the second level filter value and the third level filter value is significant, the system will
detect a touch. When a touch is detected, there are a couple of effects: the third level filter output becomes fixed (refer to
counts. When the difference between the second level filter value and the third level filter value is significant, the system will
detect a touch. When a touch is detected, there are a couple of effects: the third level filter output becomes fixed (refer to
), an interrupt is generated (refer to
), and the touch status register (
) is updated.
The touch detection system is controlled using two threshold registers for each independent electrode. The Touch Threshold
register represents the delta at which the system will trigger a touch. The Release Threshold represents the difference at which
a release would be detected. In either case the system will respond by changing the previously mentioned items.
register represents the delta at which the system will trigger a touch. The Release Threshold represents the difference at which
a release would be detected. In either case the system will respond by changing the previously mentioned items.
9.2.1
The Touch Threshold Register is used to set the touch threshold for each of the electrodes. The address of the ELE0 Touch
Threshold Register is 0x29. The address of the ELE1 Touch Threshold Register is 0x2B. The address of the ELE2 Touch
Threshold Register is 0x2D.
Threshold Register is 0x29. The address of the ELE1 Touch Threshold Register is 0x2B. The address of the ELE2 Touch
Threshold Register is 0x2D.
Figure 30. Touch Threshold Register
9.2.2
The Release Threshold Register is used to set the release threshold for each of the electrodes. The address of the ELE0 Release
Threshold Register is 0x2A. The address of the ELE1 Release Threshold Register is 0x2C. The address of the ELE2 Release
Threshold Register is 0x2E.
Threshold Register is 0x2A. The address of the ELE1 Release Threshold Register is 0x2C. The address of the ELE2 Release
Threshold Register is 0x2E.
Figure 31. Release Threshold Register
7
6
5
4
3
2
1
0
R
TTH
W
Reset:
0
0
0
0
0
0
0
0
= Unimplemented
Table 17. Touch Threshold Register Field Descriptions
Field
Description
7:0
TTH
Touch Threshold – The Touch Threshold Byte sets the trip point for detecting a
touch.
00000000 Encoding 0
~
11111111 Encoding 255
touch.
00000000 Encoding 0
~
11111111 Encoding 255
7
6
5
4
3
2
1
0
R
RTH
W
Reset:
0
0
0
0
0
0
0
0
= Unimplemented
Table 18. Release Threshold Register Field Descriptions
Field
Description
7:0
RTH
Release Threshold – The Release Threshold Byte sets the trip point for detecting
a touch.
00000000 Encoding 0
~
11111111 Encoding 255
a touch.
00000000 Encoding 0
~
11111111 Encoding 255