CAP1133 datasheet(34/63 Pages) MICROCHIP

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CAP1133

DS00001625B-page 34

 2015 Microchip Technology Inc.

Note 6-1

Recalibration Samples refers to the number of samples that are measured and averaged before the

Base Count is updated however does not control the base count update period.

Note 6-2

Update Time refers to the amount of time (in polling cycle periods) that elapses before the Base

Count is updated. The time will depend upon the number of channels active, the averaging setting,

and the programmed cycle time.

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 - 32h 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.

64 (default)

128

256

1024

256

2048

256

4096

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

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 6-31:

CAL_CFG BIT DECODE (CONTINUED)

CAL_CFG[2:0]

Recalibration Samples

(see Note 6-1)

Update Time (see

Note 6-2)

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