CAP1293 Datasheet, PDF (16/63 Pages) Microchip Technology – 3-Channel Capacitive Touch Sensor with Proximity

CAP1293
4.3.1.2 Standby State Sensing Settings
The Standby state is used for standby operation. In general, fewer sensor inputs are enabled, and they are programmed
to have more sensitivity. Sensor inputs being monitored are determined by the Standby Channel Register (see Section
5.21, "Standby Channel Register"). Sensitivity is controlled by the Standby Sensitivity Register (see Section 5.23,
"Standby Sensitivity Register"). Averaging, sample time, and cycle time are controlled by the Averaging and Sampling
Configuration Register (see Section 5.22, "Standby Configuration Register"). There is one touch detection threshold,
which applies to all sensors enabled in Standby, as defined in the Standby Threshold Register (see Section 5.24,
"Standby Threshold Register").
4.3.1.3 Combo State Sensing Settings
The Combo state is used when a combination of proximity detection and normal button operation is required. When the
COMBO bit is set, the sensing cycle includes sensor inputs enabled in the Active state as well as sensor inputs enabled
in the Standby state. Sensor inputs enabled in the Active state will use the Active settings described in Section 4.3.1.1,
"Active State Sensing Settings". Sensor inputs enabled in the Standby state will use the Standby settings described in
Section 4.3.1.2, "Standby State Sensing Settings". If a sensor input is enabled in both the Active state and in the Standby
state, the Active state settings will be used in Combo state. The programmed cycle time is determined by STBY_CY_-
TIME[1:0].
The Combo state also has two gain settings. When the COMBO bit is set, the GAIN[1:0] control only applies to the sen-
sors enabled in the Active state, and the C_GAIN[1:0] control applies to the sensors enabled in the Standby state.
4.3.2 SENSING CYCLE
Except when in Deep Sleep, the device automatically initiates a sensing cycle and repeats the cycle every time it fin-
ishes. The cycle polls through each enabled sensor input starting with CS1 and extending through CS3. As each capac-
itive touch sensor input is polled, its measurement is compared against a baseline “not touched” measurement. If the
delta measurement is large enough to exceed the applicable threshold, a touch is detected and an interrupt can be gen-
erated (see Section 4.9.2, "Capacitive Sensor Input Interrupt Behavior").
The sensing cycle time is programmable (see Section 5.10, "Averaging and Sampling Configuration Register" and Sec-
tion 5.22, "Standby Configuration Register"). If all enabled inputs can be sampled in less than the cycle time, the device
is placed into a lower power state for the remainder of the sensing cycle. If the number of active sensor inputs cannot
be sampled within the specified cycle time, the cycle time is extended and the device is not placed in a lower power
state.
4.4 Sensor Input Calibration
Calibration sets the Base Count Registers(Section 5.25, "Sensor Input Base Count Registers") which contain the “not
touched” values used for touch detection comparisons. Calibration automatically occurs after a power-on reset (POR),
when sample time is changed, when the gain is changed, when the calibration sensitivity is changed, and whenever a
sensor input is newly enabled (for example, when transitioning from a power state in which it was disabled to a power
state in which it is enabled). During calibration, the analog sensing circuits are tuned to the capacitance of the untouched
pad. Then, samples are taken from each sensor input so that a base count can be established. After calibration, the
untouched delta counts are zero.
APPLICATION NOTE: During the calibration routine, the sensor inputs will not detect a press for up to 200ms and
the Sensor Base Count Register values will be invalid. In addition, any press on the
corresponding sensor pads will invalidate the calibration.
The host controller can force a calibration for selected sensor inputs at any time using the Calibration Activate and Status
RegisterSection 5.10.1, "Calibration Activate and Status Register". When a bit is set, the corresponding capacitive touch
sensor input will be calibrated (both analog and digital). The bit is automatically cleared once the calibration routine has
successfully finished.
If analog calibration fails for a sensor input, the corresponding bit is not cleared in the Calibration Activate and Status
Register, and the ACAL_FAIL bit is set in the General Status Register(Section 5.2, "Status Registers"). An interrupt can
be generated. Analog calibration will fail if a noise bit is set or if the calibration value is at the maximum or minimum
value. If digital calibration fails to generate base counts for a sensor input in the operating range, which is +12.5% from
the ideal base count (see TABLE 4-1:), indicating the base capacitance is out of range, the corresponding BC_OUTx bit
is set in the Base Count Out of Limit Register(Section 5.17, "Base Count Out of Limit Register"), and the BC_OUT bit
is set in the General Status Register (Section 5.2, "Status Registers"). An interrupt can be generated. By default, when
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