CAP1128 datasheet(46/75 Pages) MICROCHIP

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CAP1128

DS00001622B-page 46

 2015 Microchip Technology Inc.

6.18

Sensor Input Threshold Registers

The Sensor Input Threshold registers store the delta threshold that is used to determine if a touch has been detected.

When a touch occurs, the input signal of the corresponding sensor pad changes due to the capacitance associated with

a touch. If the sensor input change exceeds the threshold settings, a touch is detected.

When the BUT_LD_TH bit is set (see Section 6.17 - bit 7), writing data to the Sensor Input 1 Threshold register will

update all of the sensor input threshold registers (31h - 37h inclusive).

6.19

Sensor Input Noise Threshold Register

The Sensor Input Noise Threshold register controls the value of a secondary internal threshold to detect noise and

improve the automatic recalibration routine. If a capacitive touch sensor input exceeds the Sensor Input Noise Threshold

but does not exceed the sensor input threshold, it is determined to be caused by a noise spike. That sample is not used

by the automatic re-calibration routine. This feature can be disabled by setting the DIS_DIG_NOISE bit.

Bits 1-0 - CS1_BN_TH[1:0] - Controls the noise threshold for all capacitive touch sensor inputs, as shown in Table 6-34.

The threshold is proportional to the threshold setting.

TABLE 6-32:

SENSOR INPUT THRESHOLD REGISTERS

ADDR

R/W

Default

30h

R/W

Sensor Input 1

Threshold

-64

40h

31h

R/W

Sensor Input 2

Threshold

-64

40h

32h

R/W

Sensor Input 3

Threshold

-64

40h

33h

R/W

Sensor Input 4

Threshold

-64

40h

34h

R/W

Sensor Input 5

Threshold

-64

40h

35h

R/W

Sensor Input 6

Threshold

-64

40h

36h

R/W

Sensor Input 7

Threshold

-64

40h

37h

R/W

Sensor Input 8

Threshold

-64

40h

TABLE 6-33:

SENSOR INPUT NOISE THRESHOLD REGISTER

ADDR

R/W

B5B4

B3B2

B1B0

Default

38h

R/W

Sensor Input

Noise Threshold

CS_BN_TH [1:0]

01h

TABLE 6-34:

CSX_BN_TH BIT DECODE

CS_BN_TH[1:0]

Percent Threshold Setting

25%

37.5% (default)

50%

62.5%

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