STMPE1601TBR STMICROELECTRONICS [STMicroelectronics], STMPE1601TBR Datasheet - Page 52

• Manufacturer Part Number: STMPE1601TBR
• Description: 16-bit enhanced port expander with keypad and PWM controller Xpander Logic
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Keypad combination key registers
52/58
Resistance
The maximum resistance between keypad outputs and inputs, inclusive of switch resistance,
protection circuit resistance and connection, must be less than 3.2 KΩ
Using the keypad controller
It is not necessary to explicitly enable the internal pull-up and direction by configuring the
GPIO control registers. Once a GPIO is enabled for the keypad function, its internal pull-up
and direction is controlled automatically.
The scanning of column inputs should then be enabled for those GPIO ports that are
configured as keypad inputs by writing '1's to the corresponding bits in the KPC_COL
register. If any of the first three column inputs is to be used as dedicated key input, the
corresponding bits in the KPC_CTRL_MSB register should be set to '1'. The bits in the
KPC_ROW_MSB and KPC_ROW_LSB registers should also be set correctly to enable the
row output scanning for the corresponding GPIO ports programmed as keypad outputs.
The scan count and de-bounce count should also be programmed into the keypad control
registers before enabling the keypad controller operation. To enable the keypad controller
operation, the EN_KPC bit in the system control register must be set to '1' to provide the
required clock signals. The keypad controller will then start its operation by setting the
SCAN bit in the KPC_CTRL_LSB register to '1'.
The keypad controller operation can be disabled by setting the SCAN bit back to '0'. To
further reduce the power consumption, the clock signals can be cut off from the keypad
controller by setting the EN_KPC bit to '0'.
As long as there is any un-read key-press in the keypad controller buffer, the KPC interrupt
will always be asserted.
Ghost key handling
The ghost key is an inherent in keypad matrix that is not equipped with a diode at each of
the keys. While it is not possible to avoid ghost key occurrence, the STMPE1601 allows the
detection of possible ghost keys by the capability of detecting 3 simultaneous key-presses in
the key matrix.
The ghost key is only possible if 3 keys are pressed and held down together in a keypad
matrix. If 3 keys are reported by the STMPE1601 keypad controller, it indicates a potential
ghost key situation. The system may check for the possibility of a ghost key by analyzing the
coordinates of the 3 keys. If the 3 keys form 3 corners of a rectangle, it could be a ghost key
situation.
A ghost key may also occur in the “special function keys”. The keypad controller does not
attempt to avoid the occurrence of ghost keys. However, the system should be aware that if
more than one special function key is reported, then there is a possibility of ghost keys.
Key detection priority
A dedicated key is always detected, if this is enabled. When a special function key is
detected, the matrix key scanning on the same input line is disabled.
Up to 3 matrix keys can be detected. Matrix keys that fall on activated special function keys
will not be counted.
As a result of these priority rules, a matrix key is ignored by the keypad controller when the
special function key on the same input line is detected, even if the matrix key is being
STMPE1601