参数资料
型号: KITMPR084EVM
厂商: Freescale Semiconductor
文件页数: 17/40页
文件大小: 0K
描述: KIT EVAL 8-PAD TOUCH MPR084
标准包装: 1
传感器类型: 触摸,电容式
接口: I²C
电源电压: 1.8 V ~ 3.6 V
嵌入式: 是,其它
已供物品: 板,缆线,CD
已用 IC / 零件: MPR084
产品目录页面: 2808 (CN2011-ZH PDF)
相关产品: MPR084EJR2CT-ND - IC CTLR TOUCH SENSR PROX 16TSSOP
MPR084QR2-ND - IC CTLR TOUCH SENSOR PROX 16-QFN
MPR084Q-ND - IC CTLR TOUCH SENSOR PROX 16-QFN
MPR084EJR2TR-ND - IC CTLR TOUCH SENSR PROX 16TSSOP
MPR084EJ-ND - IC CTLR TOUCH SENSR PROX 16TSSOP
MPR084
Sensors
24
Freescale Semiconductor
8Calibration
8.1
Introduction
The MPR084 is self-calibrating. This is done both at initial start-up of the device and during run time.
8.2
Initial Start-up Conditions
Initial calibration of the MPR084 occurs every time the device resets. The first key detection cycle is used as a baseline
capacitance value for all remaining calculations. Thus, a touch is detected by taking the difference between this baseline value
and the current capacitance on the electrode.
8.3
Auto-Calibration
The MPR084 has an auto-calibration feature. This is enabled through the Touch Pad Configuration Register (Section 3.4), by
setting the ACE bit high. Auto calibration is done by two mechanisms. The basic auto-calibration will recalculate the baseline
value after 6 sample periods. Thus the auto calibrate period can be calculate by multiplying the master clock period (in
milliseconds) and the touch acquisition sample period with a factor of 64.
Equation 6
If a touch is currently being detected the auto-calibration will not engage and calibration will be ignored. The device can also be
calibrated when a key is being touched, this is controlled by stuck key detection.
8.4
Stuck Key Detection
The Stuck Key Detection system allows the application to specify the maximum amount of time a touch should be detected before
it is calibrated into the baseline and the touch is ignored. This is controlled by setting the Stuck Key Timeout multiplication factor
(SKT). The timeout period can be calculated by multiplying the SKT, master clock period (in ms) and touch acquisition sample
period with a factor of 64.
Equation 7
When Stuck Key Detection is off a touched key will remain touched indefinitely and never be calibrated into the baseline value.
8.4.1
Stuck Key Timeout Register
The Stuck Key Timeout Register is used to determine the electrode scan period of the system. The I2C slave address of the Stuck
Key Timeout Register is 0x12.
Figure 27. Stuck Key Timeout Register
7
6
543210
R
SKT
W
Reset:
0
000000
= Unimplemented
Table 16. Stuck Key Timeout Register Field Descriptions
Field
Description
7:0
SKT
Stuck Key Timeout – The Stuck Key Timeout field selects or reports the
multiplication factor that is used to determine how often electrodes are calibrated
while a touch is being detected.
00000000 Encoding 0 – Turns off Stuck Key Detection
00000001 Encoding 1 – Sets the SKT multiplication factor to 2
~
11111111 Encoding 255 – Sets the SKT multiplication factor to 256
AutoCalibrationPeriod ms
MCP
TASP
64
=
AutoCalibrationPeriod ms
MCPTASPSKT
64
=
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