pca8885 NXP Semiconductors, pca8885 Datasheet - Page 12

• Manufacturer Part Number: pca8885
• Description: Capacitive 8-channel Proximity Switch With Auto-calibration And Very Low Power Consumption
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA8885
Objective data sheet
10.2.1.3 Key-press modes
10.2.2.1 Interrupt output INT
10.2.2 Interrupt generation
Direct mode — In direct mode, the sensor state is directly reflected in the SENS register.
When the sensor is activated, the corresponding bit in the SENS register is immediately
set logic 1. When the sensor is released, the bit is cleared (set logic 0) again. The bits are
even cleared if the SENS register has not yet been read by the system controller.
Latching mode — In latching mode, every activated sensor sets the corresponding bit in
the SENS register logic 1. When the sensor is released, the SENS register is unaffected.
Reading the SENS register clears (set logic 0) those bits, whose sensor is not activated
anymore.
After reset, the PCA8885 is set to direct switching mode.
There are three key-press modes implemented in the PCA8885: N-key, 1-key, and 2-key
mode.
N-key mode — In N-key mode, each sensor activity is reflected in register SENS
according to the configured switching mode. The N-key mode is the default key-press
mode after reset.
1-key mode — In 1-key mode, only the first sensor activation sets the corresponding bit
in register SENS. All further activations of the other sensors are suppressed at the SENS
register boundary. In this way, sensors in a keypad are masked out, which are activated
accidentally because they are arranged next to the activated sensor.
The 1-key mode supports sensor matrix arrangements with two PCA8885, where one chip
is attached to the columns and one to the rows (primary-chip and secondary-chip). Sensor
activation sets 1 bit for the column and 1 bit for the row in the SENS register of the
appropriate chip. Each activation of a sensor raises an interrupt. The system controller
must handle the situation where the INT is raised before the second sensor in the matrix
has been activated.
2-key mode — In 2-key mode, only the two first sensor activations set the corresponding
bits in register SENS. All further activations of the other sensors are suppressed at the
SENS register boundary. This mode supports in particular the matrix arrangement of
sensors using only one PCA8885, as illustrated in
sensors in a matrix are masked out, which are activated accidentally because they are
arranged next to the intended sensors. This mode properly handles a delay in sensor
activation due to unequal sensor capacitance or area (non-centric sensor touching, and
so on) as long as the intended sensors react before sensors which are activated
accidentally. In 2-key mode, the INT output is only activated after 2 bits have been set in
the SENS register.
The PCA8885 provides two mechanisms to inform the system controller that a sensor
activity has been detected.
The PCA8885 has an interrupt output, INT, to flag to the system controller that a
capacitive event has been detected. The controller can then fetch the sensor state by
reading the SENS register over the I
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 24 November 2011
Capacitive 8-channel proximity switch with auto-calibration
2
C-bus.
Figure 25 on page
34. In this way,
PCA8885
© NXP B.V. 2011. All rights reserved.
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