CAP1188 Datasheet, PDF (35/79 Pages) Microchip Technology – 8 Channel Capacitive Touch Sensor with 8 LED Drivers

CAP1188
6.4 Sensor Input Delta Count Registers
TABLE 6-6: SENSOR INPUT DELTA COUNT REGISTERS
ADDR R/W
Register
B7
B6
B5
B4
B3
B2
B1
B0
Default
10h
R
Sensor Input 1
Delta Count
Sign
64
32
16
8
4
2
1
00h
11h
R
Sensor Input 2
Delta Count
Sign
64
32
16
8
4
2
1
00h
12h
R
Sensor Input 3
Delta Count
Sign
64
32
16
8
4
2
1
00h
13h
R
Sensor Input 4
Delta Count
Sign
64
32
16
8
4
2
1
00h
14h
R
Sensor Input 5
Delta Count
Sign
64
32
16
8
4
2
1
00h
15h
R
Sensor Input 6
Delta Count
Sign
64
32
16
8
4
2
1
00h
16h
R
Sensor Input 7
Delta Count
Sign
64
32
16
8
4
2
1
00h
17h
R
Sensor Input 8
Delta Count
Sign
64
32
16
8
4
2
1
00h
The Sensor Input Delta Count registers store the delta count that is compared against the threshold used to determine
if a touch has been detected. The count value represents a change in input due to the capacitance associated with a
touch on one of the sensor inputs and is referenced to a calibrated base “Not Touched” count value. The delta is an
instantaneous change and is updated once per sensor input per sensing cycle (see Section 5.5.1, "Sensing Cycle").
The value presented is a standard 2’s complement number. In addition, the value is capped at a value of 7Fh. A reading
of 7Fh indicates that the sensitivity settings are too high and should be adjusted accordingly (see Section 6.5).
The value is also capped at a negative value of 80h for negative delta counts which may result upon a release.
6.5 Sensitivity Control Register
TABLE 6-7: SENSITIVITY CONTROL REGISTER
ADDR R/W
Register
B7
B6
B5
B4
1Fh
R/W
Sensitivity Control
-
DELTA_SENSE[2:0]
B3
B2
B1
B0
BASE_SHIFT[3:0]
Default
2Fh
The Sensitivity Control register controls the sensitivity of a touch detection.
Bits 6-4 DELTA_SENSE[2:0] - Controls the sensitivity of a touch detection. The sensitivity settings act to scale the rel-
ative delta count value higher or lower based on the system parameters. A setting of 000b is the most sensitive while a
setting of 111b is the least sensitive. At the more sensitive settings, touches are detected for a smaller delta capacitance
corresponding to a “lighter” touch. These settings are more sensitive to noise, however, and a noisy environment may
flag more false touches with higher sensitivity levels.
APPLICATION NOTE: A value of 128x is the most sensitive setting available. At the most sensitivity settings, the
MSB of the Delta Count register represents 64 out of ~25,000 which corresponds to a touch
of approximately 0.25% of the base capacitance (or a C of 25fF from a 10pF base
capacitance). Conversely, a value of 1x is the least sensitive setting available. At these
settings, the MSB of the Delta Count register corresponds to a delta count of 8192 counts
out of ~25,000 which corresponds to a touch of approximately 33% of the base capacitance
(or a C of 3.33pF from a 10pF base capacitance).
 2015 Microchip Technology Inc.
DS00001620C-page 35