MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 36

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

MPR121
36
FILTERED DATA LOW
BASELINE VALUE
the threshold. Since this calculation is done totally internal to the part, it is unnecessary for the user to actually do this math in
the software. If it were being done, the steps would be to first combine the Filtered Data Low and Filtered Data High values into
a single 10-bit number. Thus,
disregarded for output. The Touch Threshold is a user defined value. There is both a touch and an un-touch threshold to provide
hysteresis.
In this system, a touch is defined as any time the difference between the Filtered Data and the Baseline Value is greater than
The baseline is then shifted to the left to make it equal scale to the Data.
Internally to the device, the full 10-bit value is stored, but as this level of precision is not necessary as the low two bits are
Table 29. Filtered Data Low Register Field Descriptions
Table 30. Filtered Data High Register Field Descriptions
Reset:
Reset:
FDLB
Field
Field
7:0
7:0
BV
W
W
R
R
7
0
7
0
Data = Filtered Data High • 256 + Filtered Data Low
= Unimplemented
= Unimplemented
Filtered Data Low Byte – The Filtered Data Low Byte displays the lower 8 bits of
the 10 bit filtered A/D reading.
00000000 Encoding 0
~
11111111 Encoding 255
Baseline Value – The Baseline Value byte displays the higher 8 bits of the 10 bit
baseline value.
00000000 Encoding 0 – The 10 bit baseline value is between 0 and 3.
~
11111111 Encoding 255 – The 10 bit baseline value is between 1020 and 1023.
6
0
6
0
Figure 42. Filtered Data High Register
Figure 41. Filtered Data Low Register
Baseline = Baseline Value • 4
5
0
5
0
4
0
4
0
FDLB
BV
Description
Description
3
0
3
0
2
0
2
0
1
0
1
0
Freescale Semiconductor
0
0
0
0
Sensors