AN3245 Datasheet, PDF (17/19 Pages) STMicroelectronics – A hardware and software guide for the STMPE1801 Xpander

AN3245
Software
2.2.4
Key lock with combination keys
STMPE1801 provides key lock features when a combination key is defined. Without a
programmed combination key, this feature is not active. Once activated all subsequent key
presses are ignored. Key lock remains until a combination keys press is detected.
Key lock is enabled when:
1. Bit[1] of the KPC_CMD register is written '1' and
2. All keys are released.
Read back of '1' at bit [1] of the KPC_CMD register only means that the key lock command
is active. It doesn't mean that the device has already entered into key lock mode.
Read back of '0' at bit [1] of the KPC_CMD register means that the key lock command is not
active or the device has exited from key lock mode.
2.3
Hotkey de-bounce
It is possible that a signal from a mechanical connector (e.g. a 3.5 mm earphone jack) is
connected to the STMPE1801 input as a hotkey input. In such a case, excessive noise is
expected from the hotkey input due to the mechanical movement.
STMPE1801 provides a programmable hotkey de-bounce ranging from 30 µs to 210 µs
(SYS_CTRL Register 0x02). If this is not sufficient, it is also possible to connect the noise
input to one of the 4 dedicated keys (GPIO_0, GPIO_1, GPIO_2, and GPIO_3 pins) to which
de-bounce can be programmed from 10 ms to 127 ms (KPC_CTRL_MID Register 0x34).
If the above de-bounce is still not sufficient, the host can implement the filtering or de-
bouncing by polling the status bit in the interrupt status register (0x09).
2.4
Power modes transition
Table 3 highlights the states of keypad FIFO, GPIO, Interrupt, and PWM during the various
power modes:
– Operational mode
– Hibernation mode
– Reset
Table 3. Power modes vs. GPIO/Keypad/Interrupt data
Operational
mode
Hibernation mode
Keypad configuration
and FIFO data
GPIO configuration, pin
state, and data
Active
Active
Sustained
(FIFO is read and cleared
prior to entering
hibernation mode)
Sustained
Interrupt configuration
and data
Active
Sustained
Reset (HW, SW, POR,
general call)
Cleared
Cleared
Cleared
Doc ID 17747 Rev 1
17/19