CAP1208 datasheet(24/67 Pages) MICROCHIP

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8-Channel Capacitive Touch Sensor

Datasheet

DS00001570B-page 24

 2014 Microchip Technology Inc.

"Configuration Registers") is set to 0, the Noise Flag Status bit for the capacitive sensor input is set if

any analog noise is detected. If the SHOW_RF_NOISE bit is set to 1, the Noise Flag Status bits will

only be set if RF noise is detected.

The CAP1208 offers optional noise filtering controls for both analog and digital noise.

For analog noise, there are options for whether the data should be considered invalid. By default, the

DIS_ANA_NOISE bit (see Section 5.6.1, "Configuration - 20h") will block a touch on a sensor input if

low frequency analog noise is detected; the sample is discarded. By default, the DIS_RF_NOISE bit

(see Section 5.6.2, "Configuration 2 - 44h") will block a touch on a sensor input if RF noise is detected;

the sample is discarded.

For digital noise, sensor input noise thresholds can be set (see Section 5.20, "Sensor Input Noise

Threshold Register"). If a capacitive touch sensor input exceeds the Sensor Noise Threshold but does

not exceed the touch threshold (Sensor Threshold (see Section 5.19, "Sensor Input Threshold

Registers") in the Active state or Sensor Standby Threshold in the Standby state (Section 5.24,

"Standby Threshold Register")), it is determined to be caused by a noise spike. The DIS_DIG_NOISE

bit (see Section 5.6.1, "Configuration - 20h") can be set to discard samples that indicate a noise spike

so they are not used in the automatic recalibration routine (see Section 4.4.1, "Automatic

Recalibration").

4.8

Interrupts

Interrupts are indicated by the setting of the INT bit in the Main Control Register (see Section 5.1,

"Main Control Register") and by assertion of the ALERT# pin. The ALERT# pin is cleared when the

INT bit is cleared by the user. When the INT bit is cleared by the user, status bits may be cleared (see

Section 5.2, "Status Registers").

4.8.1

ALERT# Pin

The ALERT# pin is an active low output that is driven when an interrupt event is detected.

4.8.2

Capacitive Sensor Input Interrupt Behavior

Each sensor input can be programmed to enable / disable interrupts (see Section 5.12, "Interrupt

Enable Register").

When enabled for a sensor input and the sensor input is not the designated power button, interrupts

are generated in one of two ways:

1. An interrupt is generated when a touch is detected and, as a user selectable option, when a release

is detected (by default - see INT_REL_n in Section 5.6.2, "Configuration 2 - 44h"). See Figure 4.4.

2. If the repeat rate is enabled then, so long as the touch is held, another interrupt will be generated

based on the programmed repeat rate (see Figure 4.3).

When the repeat rate is enabled for a sensor input (see Section 5.13, "Repeat Rate Enable Register"),

the device uses an additional control called MPRESS that determines whether a touch is flagged as

a simple “touch” or a “press and hold” (see Section 5.9, "Sensor Input Configuration 2 Register"). The

MPRESS[3:0] bits set a minimum press timer. When the button is touched, the timer begins. If the

sensor pad is released before the minimum press timer expires, it is flagged as a touch and an

interrupt (if enabled) is generated upon release. If the sensor input detects a touch for longer than this

timer value, it is flagged as a “press and hold” event. So long as the touch is held, interrupts will be

generated at the programmed repeat rate (see Section 5.8, "Sensor Input Configuration Register") and

upon release (if enabled).

If a sensor input is the designated power button, an interrupt is not generated as soon as a touch is

detected and repeat rate is not applicable. See Section 4.8.3, "Interrupts for the Power Button".

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