CAP1298 datasheet(45/68 Pages) MICROCHIP

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DS00001571B-page 45

CAP1298

Note 5-2

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

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

and the programmed sensing cycle time.

5.19

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 5.18 - bit 7), writing data to the Sensor Input 1 Threshold register will

update all of the Sensor Input Threshold registers (31h - 37h inclusive).

5.20

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 recalibration 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 5-3.

The threshold is proportional to the threshold setting.

TABLE 5-1:

SENSOR INPUT THRESHOLD REGISTERS

Addr

R/W

B5B4

B3B2

B1B0

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 5-2:

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

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