CAP1133 datasheet(17/63 Pages) MICROCHIP

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DS00001625B-page 17

CAP1133

5.3.6

RF NOISE DETECTION

Each sensor input contains an integrated RF noise detector. This block will detect injected RF noise on the CS pin. The

detector threshold is dependent upon the noise frequency. If RF noise is detected on a CS line, that sample is removed

and not compared against the threshold.

5.4

ALERT# Pin

The ALERT# pin is an active low (or active high when configured) output that is driven when an interrupt event is

detected.

Whenever an interrupt is generated, the INT bit (see Section 6.1, "Main Control Register") is set. The ALERT# pin is

cleared when the INT bit is cleared by the user. Additionally, when the INT bit is cleared by the user, status bits are only

cleared if no touch is detected.

5.4.1

SENSOR INTERRUPT BEHAVIOR

The sensor interrupts are generated in one of two ways:

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

(by default - see Section 6.6). See Figure 5-3.

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 5-2).

When the repeat rate is enabled, the device uses an additional control called MPRESS that determines whether a touch

is flagged as a simple “touch” or a “press and hold”. 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 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 and upon release (if enabled).

APPLICATION NOTE: Figure 5-2 and Figure 5-3 show default operation which is to generate an interrupt upon

sensor pad release and an active-low ALERT# pin.

APPLICATION NOTE: The host may need to poll the device twice to determine that a release has been detected.

FIGURE 5-2:

Sensor Interrupt Behavior - Repeat Rate Enabled

Touch Detected

INT bit

Button Status

Write to INT bit

Polling Cycle

(35ms)

Min Press Setting

(280ms)

Interrupt on

Touch

Button Repeat Rate

(175ms)

Button Repeat Rate

(175ms)

Interrupt on

Release

(optional)

ALERT# pin

(active low)

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